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The Bronsted acid-catalyzed Diels-Alder reaction was examined. Phosphoric acids were effective Bronsted acids for the Diels-Alder reaction of cyclohexadienones and activated by the internal hydrogen-bonding of the adjacent hydroxy group.

The reaction between an α-pyridinium acetamide bearing an 8-phenylmenthyl group as the chiral auxiliary and β-substituted methylidenemalononitriles gave rise to trans-cyclopropanes with diastereomeric ratios of up to 98:2. For most of the reactions, the absolute stereochemistry of the major product was found to be opposite of that of the major products of the reaction of the corresponding ester series, which also utilized the 8-phenylmenthyl group.

The cyclopropanation of (−)-8-phenylmenthyl (E)-3-aryl-2-phosphonoacrylates with dimethyloxosulfonium methylide and diazomethane afforded the corresponding trans cyclopropane derivatives with high diastereoselectivity as the major diastereomer. The high selectivity is understandable in terms of the π–π interaction between the phenyl ring of the chiral auxiliary and the acrylate moiety.

The reaction of various mono-substituted methylidenemalononitriles with (−)-8-phenylmenthyl α-pyridiniumacetate in the presence of base afforded the corresponding dicyanocyclopropane compounds with exclusive trans -selectivity and good diastereoselectivity (up to 86:14). The stereochemistry of the major products were determined to be of 1 R configuration by X-ray structural analysis of the crystalline trans -2,2-dicyano-3-(4-pyridyl)cyclopropanecarboxylate. The geometric and diastereofacial selectivities were rationalized assuming anti -periplanar approach in the open-chain model, followed by epimerization and then cyclization to give the cyclopropane compounds.

The essentially complete (>99%) asymmetric Diels-Alder reactions were achieved between 3-(8-phenylmenthyloxycarbonyl)coumarin ( 1c ) and 1,3-butadienes ( 2a–c ) in high chemical yields.

The reactions of allylstannanes with 4-siloxy-1-benzopyrylium salts gave the corresponding allylated derivatives more smoothly than allylsilanes. Similar reactions with 3-trimethylsilyl-1-butene afforded unexpected five-membered ring adducts in 87% and 37% yields, respectively.

Asymmetric Darzens condensation of benzaldehyde and various ketones has been investigated. The condensation of acetophenone, propiophenone and symmetric ketones with (–)-8-phenylmenthyl halogenoacetates 3a,b afforded the corresponding glycidic esters cis-12, cis-13 and 15–19 in 77–96% de, respectively, as the major products. Aza-Darzens condensation between N-benzylideneaniline and 3a occurred to give the trans-aziridine 21 as the major isomer in >85% de. The stereochemistry of the major diastereoisomers of cis-12 and 18 was confirmed by their conversion into the known optically active diols 22 and 24. The configuration of the major product of cis-12 was determined to be 2R,3R and that of 18 to be 2R. The geometric and disastereofacial selectivities were understandable in terms of the open-chain or non-chelated antiperiplanar transition state model in the initial aldol-type reaction.

Ring-expansion of methyl 2-bromomethyl-5-oxiranylpent-2-enoate (7) with various acids was studied; treatment with Lewis acids (TiBr4, MgBr2 and ZnBr2) afforded the tetrahydrofuran derivative 4-Br as a major product, while reaction with silver salt (AgNO3/KPF6), which is known to have a high halide affinity, gave preferentially the tetrahydropyran 3-ONO2 derivatives as the major products.

Various 3-sulfonyl-1,2,4-triazole-1-carboxamides (5a–h) were synthesized and their hydrophobicities were evaluated from their retention time in reversed-phase HPLC chromatography. Although the compounds have rather complex structures, a good linear relationship was observed between log k′ of these compounds derived from the retention time of HPLC and log PH for water–hexadecane partition coefficients of related alcohols. In regards with the rotation about the O2S–C(ester part) single bond, the preference for a gauche conformer relative to the anti form was revealed by both X-ray structural analysis of 5a and calculations at the AM1 level. In this conformation, substituents are arrayed to have the largest separation between the hydrophilic and hydrophobic parts. This can be rationalized as the primary reason for the good linearity.

With the purpose of developing a method of preparing Z-alpha,beta-unsaturated amides, the Peterson reaction of the (triphenylsilyl)acetamide Ph(3)SiCH(2)COX (1, X = NBn(2); 3, X = NMe(2)) with various aldehydes was examined. The reaction of aromatic aldehydes gave selectivities up to >97:3. It was found that the selectivity was a function of the electronic nature of the aromatic ring and higher Z selectivity was attained with electron-rich aldehydes. With aliphatic aldehydes selectivities up to 92:8 were achieved, and unlike with analogous phosphorus reagents, less sterically hindered aldehydes gave higher Z selectivity. Also, 3, which has a smaller amide group than 1, tended to give rise to higher selectivity. A comparison with the reaction of trimethylsilyl analogues revealed the significance of the phenyl substituents on the silyl group.

The mechanism we propose for the cyclopentane annulation is the following one. The allylic reagent (5D) attacks the siloxypyrylium salts (2a,b) at the C2 position, giving the intermediate carbocation (B) which is stabilized by the trimethylsilyl and the methyl group. Attack by the emerging enolate at C 3 , forms the five-membered ring compound (8a,b). Generally, electrophiles attack allylic silanes anti to the silyl group. Since there is undoubtedly interaction with the silicon in the transition state, the stereochemistry of the bridged intermediate (B) should be trans geometry due to stereoelectronic effect and allylic 1,3-strain. In the reaction of 2a, the favored pathway is cyclization. However, competition between cyclization and desilylation was observed in 2b due to steric hindrance between the two methyl groups at the step of cyclization

New title dibenzobicyclic stiboranes and related phosphoranes were prepared by means of tridentate 2,2′-diphenolamines. Coordination number of the central pnictogen atoms (Sb and P) changed from three into five during the reaction.

A method for the practical construction of poly-functionalized bicyclo[3.3.1]nonenones by successive Michael reactions of cyclohexenones with acrylates using K2CO3 and TBAB (n-Bu4N+ Br-) was developed. The construction could be carried out in both stepwise and one-pot reactions with similar tendencies in regioselectivity. The alpha-regioselectivity in the intramolecular Michael reaction agreed with that stereoelectronically expected in intermolecular reactions based upon consideration of the HOMO orbital profile of the enolate I, the precursor to ring-closure, although the reaction site was trisubstituted and prone to steric hindrance in most of the examples presented. For the acetoxymethylacrylates substituted at either the alpha or gamma position, steric hindrance of the substituents (R2 and R3) served as a controlling factor to induce high regiocontrol. Facial selection in the protonation of enolate II, formed upon ring-closure, was also affected by these substituents. In both the intramolecular Michael reaction and the protonation of enolate II, the ammonium counter cation played an important role.

Cinchonidine catalyzed the cyclopropanation reaction between chloromethyl ketones and β-substituted methylidenemalononitriles to give trans-cyclopropanes with enantioselectivity up to 82% ee. Experimental evidence suggests that cinchonidine functions as a chiral Bronsted base catalyst in the reaction and hydrogen bonding is essential for inducing high enantioselectivity.

Construction of the bicyclo[3.3.1]nonenone core was achieved by stepwise annulation of 2-cyclohexenone derivatives and acrylates via successive Michael reactions. The process could also be effected by a one-pot procedure.

The Peterson reaction of triphenylsilylacetamide Ph3SiCH2CONBn2 with aromatic aldehydes and certain aliphatic aldehydes proceeded to give the corresponding α,β-unsaturated amide with high Z selectivity (up to Z∶E = >97∶

The [5+2]cycloaddition reaction of 2-substituted-3-oxidopyrylium betaine with dialkyl fumarates was found to proceed with stereoselectivity up to 15.5 : 1. The stereoselectivity became higher as either the 2-substituent of the 3-oxidopyrylium or the alkoxy group of the fumarate became larger. The stereoselectivity could be rationalized by considering these steric effects.

Ring-expansion of methyl 2-bromomethyl-5-oxiranylpent-2-enoate (7) with various acids was studied; treatment with Lewis acids (TiBr4, MgBr2 and ZnBr2) afforded the tetrahydrofuran derivative 4-Br as a major product, while reaction with silver salt (AgNO3/KPF6), which is known to have a high halide affinity, gave preferentially the tetrahydropyran 3-ONO2 derivatives as the major products.

The reaction between β-substituted methylidenemalononitriles and the ylide from (-)-8-phenylmenthyl α-pyridiniumacetate, which affords activated cyclopropanes bearing two cyano groups and one carboxylic ester group, was examined. The trans isomer was obtained in up to 91:9 diastereoselectivity under optimized solvent conditions for the t-butyl substituted substrate. The selectivity increased to 96:4 upon using 4-methoxypyridine in the place of pyridine, whereas selectivities were generally lower for N,N-diethylnicotinamide. The major 4-pyridyl substituted cyclopropane was determined to be trans-1R by X-Ray structural analysis.

Selectivity of alkylation of and that of deuteration of methyl groups attached to the pyrimidine ring of tetraazathiapentalenes are discussed.

In order to construct the tetrahydropyran ring of rhopaloic acid A and hippospongic acid A, the ring-expansion of methyl 2-bromomethyl-6,7-epoxyhept-2-enoate with various acids was studied; treatment of the bromo oxirane with Lewis acids (TiBr 4 , MgBr 2 and ZnBr 2 ) afforded a tetrahydrofuran derivative as the major product, while reaction of the oxirane with silver salt (AgNO 3 /KPF 6 ) gave a tetrahydropyran derivative as the major product.

The Julia-Colonna asymmetric epoxidation reaction of substituted benzalacetophenone afforded the corresponding epoxide with high yield and high enantioselectivity, catalyzed by the specified length of poly-L-leucine (chain length n > 15). Poly-L-leucine catalysts have been prepared by the polymerization reaction of L-leucine-NCA with initiators (BnONa, n-BuNH 2 , H 2 O) and characterized by the MALDI-TOF Mass and IR analysis.

The Diels-Alder reactions of cross-conjugated ketones bearing an oxa-spiro-ring with some simple sterically undemanding dienes (cyclopentadiene, 2,3-cyclohexadiene, 2,3-dimethyl-1,3-butadiene) afforded the adduct with high π-facial selectivity under mild conditions. The π-facial selectivity can be explained in terms of Cieplak model.

The selective monochlorination of 5-[2-(N-silyl-amino)vinyl] isothia- zoles (1a,b) and their related compounds (1c,d, 2a-g, 3a-c, and 4a,b) with N-chlorosuccinimide is described. Chlorination of (1a,b) occurred at vinyl carbon to give (5a,b) and the geometry was determined to be Z-isomer according to spectral data. It is noteworthy that (1d) smoothly occurred bond switch at room temperature but (5)d did not ring-trans- form under the same conditions

In the presence of 1,4-diazabicyclo[2.2.2]octane, 5-amino-3-methylisothiazole (4a) in acetonitrile condensed with N-methyl-p-chlorobenzimidoyl chloride (5a) to afford two kinds of compounds along with several minor products. One of the two was 1 : 1 condensed product (6a) and the other was 2 : 1 condensed product (7a). The latter compound was obtained in higher yield when an excess 4a was treated with 5a. On the other hand, in the absence of the additional base, 2 : 3 condensed compound (8a) was isolated as a major product besides 6a and 7a. 8a was obtained by treatment of 7a with 2 equiv. of imidoyl chloride in 21% yield. Reaction of 5-amino-3-phenylisothiazole (4b) with imidoyl chloride (5a,b) furnished the analogous products

α-Hydroxyketones were oxidized into α-diketones with triphenylantimony dibromide in the presence of two equiv. of base. Antimony-catalyzed debromination and oxidation cycle was devised for the system of ethyl 2,3-dibromo-3-phenylpropionate and α-hydroxyketones.

6,7-Dihydro-6-methyl-5H-dibenzo[b,g][1,5]thiazocine (7) was prepared by cyclization of the corresponding amino alcohol using thionyl chloride in acetonitrile. Methylation of 7 gave N,N-dimethyl derivative (8) as the sole product. Treatment of 7 with various oxidizing reagents, however, afforded the corresponding sulfoxide (9) and/or N-oxide (13), and sulfone (14) depending on the kind of reagent. Oxidation of 7 with sodium periodate furnished N-oxide (13) in 72% yield as a major product along with sulfoxide (9) in 12% yield, while 9 was obtained as a major product (76%) by oxidation with sodium hypochlorite together with a small amount of methoxysulfonium derivative (15) in aqueous methanol. The acceleration in oxidation of 7 compared with diphenyl sulfide as well as production of 15 is ascribed to the transannular participation of the amino group with the chlorosulfonio group or intermediacy of a sulfurane. In addition, structural features of 9 and 15 have been investigated by means of 1H NMR and evidenc...

Substituents at 5-position of 5-amino-3-methyl- and 3-p-chlorophenyl-5-methylisothiazoles (7 and 8) were silylated and then lithiated to couple with aromatic nitriles in order to afford the adducts (4 and 5) via 1,3-silyl group shift. Desilylation of 5 with TBAF gave solely non-ring-transformed product (3-α-form). By using the pure sample of 3-α-form, the reversible ring-trans- formation (bond switch) was observed under neutral conditions for the first time.

While the solvolysis of tosylate 5c proceeds very rapidly to generate 4 or its rapidly equilibrating classical alternative, the epimeric compound 6c proved to be unreactive; bond orientation effects are implicated.

The rate of methyl transfer to pyridine-d5 of δ-ammoniomethylsulfurane, i.e., S,N-dimethyl-6,7-dihydro-5H-dibenzo [b,g][1,5] thiazocinium salt ( 1 ), was slower by 1300 times than that of methyldiphenylsulfonium salt ( 3 ). Activation parameters at 25 °C were obtained for 1 ,ΔH≠=23.1,ΔS≠=−7.8, and for 3 ,ΔH≠=18.1 kcal/mol,ΔS≠=−10.3 e.u., which are in accord with the hypervalent bonding of 1 .

Preparations of anti-4′-substituted 3,4-benzotricyclo[4. 3. 1. 01,6]dec-3-en-2-yl p-nitrobenzoates (1a–d) are described. The solvolysis of these esters was examined in 80% aqueous acetone. The rates were relatively high but the sensitivity to substituents on the benzene ring was low in comparison with other secondary systems. It is considered that σ-participation rather than π-conjugation might contribute to the rate accelerative effect. In the presence of a base, 1a–d gave anti-alcohol (12a–d) (13 to 17%), syn-alcohol (13a–d) (31 to 78%), and tert-alcohol (14a–d) (5 to 54%). The product distributions are explained in terms of a nonclassical homonaphthalenium cation (24).

トリフェニルアンチモンジブロミド[2a]によりα-ケトアルコール類を酸化した。こめ酸化反応は,まず最初塩基によりアピカル位の配位子(臭素)がアルコキシル基に交換しhypervalentアンチモン化合物[D]またはスチボニウム塩[E]が生じ,つぎにα-カルビニル水素が引き抜かれてトリフェニルスチビンが生じるとともにα-ジゲトンが生成する経路(1)と五員環中間体[F]を経由して酸化する経路(2)が考えられる。一方,アピカル位の基を2-ピリジニルオキシ基で置換した五価アンチモン化合物[2d]を合成した。この化合物を用いると塩基を加えることなしに非常にすみやかにかつ収率よくα-ケトアルコールをα-ジケトンに酸化できた。トリフェニルスチビン[1a]の脱臭素反応と[2a]の酸化能を組み合わせることにより,触媒量のアンチモン化合物[1a]または[2a]でα-ケトアルコールをα-ジケトンに酸化できることを見いだした。

Dibenz[c,f][1,5]azaphosphocine 12-oxide derivatives (1a, 3) and their related compounds were prepared and NMR spectral change of these samples by the addition of SOCl2 or t-BuMe2SiOTf are reported. The NMR parameters (1H and 31P) are consistent with bicyclic phosphoranes for at least 1a′ and 3′, each contains a transannular hypervalent ClPNMe bond.

6,7-Dihydro-6-methyl-5H-dibenzo[b,g][1,5]thiazocine (7) was prepared by cyclization of the corresponding amino alcohol using thionyl chloride in acetonitrile. Methylation of 7 gave N,N-dimethyl derivative (8) as the sole product. Treatment of 7 with various oxidizing reagents, however, afforded the corresponding sulfoxide (9) and/or N-oxide (13), and sulfone (14) depending on the kind of reagent. Oxidation of 7 with sodium periodate furnished N-oxide (13) in 72% yield as a major product along with sulfoxide (9) in 12% yield, while 9 was obtained as a major product (76%) by oxidation with sodium hypochlorite together with a small amount of methoxysulfonium derivative (15) in aqueous methanol. The acceleration in oxidation of 7 compared with diphenyl sulfide as well as production of 15 is ascribed to the transannular participation of the amino group with the chlorosulfonio group or intermediacy of a sulfurane. In addition, structural features of 9 and 15 have been investigated by means of 1H NMR and evidenc...

Dibenz[c,f][1,5]azaphosphocine 12-oxide derivatives (1a, 3) and their related compounds were prepared and NMR spectral change of these samples by the addition of SOCl2 or t-BuMe2SiOTf are reported. The NMR parameters (1H and 31P) are consistent with bicyclic phosphoranes for at least 1a′ and 3′, each contains a transannular hypervalent ClPNMe bond.

Die photochemische Umlagerung der bekannten Spirocyclen (I) zu den spirocyclischen Cyclopropanen (II) wird untersucht.

Reaction of silyl enol ethers (1a–f) with N-chlorosuccinimide afforded siloxycarbinyl cations which were trapped by nucleophiles (NaN3 and MeOH); subsequent rearrangement of the azido products (2a,b,d,e–N3) under reflux in decalin led to anilide derivatives (3a,b,d,e).

A novel secondary cyclopropylphenylmethyl acetate was prepared from a chromone skeleton via homochromone derivatives in order to study solvolytic behavior. Reduction of the cyclopropyl ketone (homochromone) with lithium aluminum hydride in ether to the corresponding secondary alcohol, was found to be highly stereospecific giving only one of the geometrical isomers. The alcohol was converted into its acetate and subjected to solvolysis in 80% acetone–water. The acetate was hydrolyzed at the rate of 3×10−5 s−1 (25 °C) undergoing alkyloxygen fission. This rate constant was as high as the most reactive secondary esters in solvolyses ever reported, and about 20 times as high as the corresponding carbocyclic ester by estimation of the same leaving group. Product studies were undertaken in the presence of sodium hydrogencarbonate, and seven-membered hemiacetal was obtained in good yield. The structural characteristics of the homochromenol ester in the solvolysis are discussed and benzohomopyrylium ion, an extrem...