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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.

A stereoselective total synthesis of scyphostatin is described. The hydrophilic moiety was stereoselectively synthesized via (i) a highly pi-facially selective Diels-Alder reaction of a spirolactone generated from L-tyrosine and (ii) a hydroxy group directed epoxidation as key reactions. The hydrophilic moiety was combined with the hydrophobic side chain in the final stage. Total synthesis was achieved by overcoming the instability of the C5-C6 epoxide ring with carefully executed mild reactions. In the course of this work, it was revealed that we had mistakenly assigned the relative stereochemistry of the C5-C6 epoxide ring of the end product in our previous model study. Revision of the stereochemical assignment in the model study is described. A diastereomer of (+)-scyphostatin epimeric at C5 and C6 (the epoxide region) was also synthesized.

Rhopaloic acid A (+)-1 and the related compounds (–)-ent-1 and (±)-rac-1 have been stereoselectively synthesized. The synthetic strategy consists of successive homologation of (2E,6E)-farnesol 7 and cyclization to form a tetrahydropyran ring, together with final introduction of an α-methylene group on the carboxylic moiety. The cyclization is carried out by intramolecular hetero-Michael addition leading to 2,5-disubstituted tetrahydropyrans. The stereochemistry can be rationalized by invoking a model of a chair-like transition state. The asymmetric synthesis is achieved by way of the Evans’ asymmetric alkylation procedure using (S)- or (R)-4-benzyloxazolidin-2-one as the chiral auxiliary. In the event, the configuration of natural rhopaloic acid A (+)-1 could be assigned as 2R,5S by comparison of the specific rotations of synthetic compounds with that of the natural product.

Adamantane derivatives were constructed by the one-pot reaction of ethyl 2,4-dioxocyclohexanecarboxylate with 2-phenylethyl 2-(acetoxymethyl)acrylate or 2-(acetoxymethyl)-1-phenyl-2-propen-1-one via domino Michael reactions and a Dieckmann condensation or an aldol-type reaction (four-bond formation). This is the first one-pot construction of adamantane derivatives from cyclohexanone derivatives not involving enamines.

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

The construction of a highly functionalized adamantane core of plukenetione-type polycyclic polyprenylated acylphloroglucinols (PPAPs) is described. The method features the construction of the bicyclo[3.3.1]nonane core (3) by successive Michael reactions and the construction of the adamantane core of plukenetione-type PPAPs by acid-catalyzed cyclization of a bicyclo[3.3.1]nonane precursor (2).

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.

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...

Each diastereoisomeric pair of α-(trans-2-p-tolylcyclopropyl) benzyl and α-(trans-2-phenylcyclopropyl)-p-tolylmethyl 3,5-dinitrobenzoates (I-4a, b, II-4a, b) has been synthesized. The relative solvolytic rates of I-4b to I-4a and of II-4b to II-4a in 80% aqueous acetone have been found to be 3.59 and 1.86 respectively at 25 °C. In the presence of 2,6-lutidine, the major products in the solvolysis were homoallylic alcohols.

The crystal structure of syn-[4.4.3]propella-2,4,12-trien-11-ol 3,5-dinitrobenzoate, 2, has been determined by single crystal X-ray diffraction and refined to an R value of 0.051. The crystal structure is triclinic with a = 10.208(2), b = 13.355(2), c = 7.068(1) Å, α = 99.35(1)°, β = 100.63(1)°, γ = 100.79(1)°, and the space group is [Formula: see text] with two molecules per cell, D(calcd) = 1.39 g cm−3. The unsaturated five-membered ring resides in an envelope conformation with C6—C11—C12—C13 lying essentially in a plane. The fifth atom, C1, is positioned 0.47 Å out of this plane on the side opposite O1. The latter is situated 1.38 Å away and projects the 3,5-dinitrobenzoate group above the central portion of the cyclohexadiene unit. Four contiguous carbon atoms in the latter ring are mutually coplanar and the fused cyclohexane ring adopts a chair conformation. The overall molecular geometry is reconcilable with its solvolytic behavior in aqueous acetone.

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。

It was found that the Clemmensen reduction of 2-benzoylcyclopentene-1-carboxylic acid (2a) did not give rise to 2-benzylcyclopentene-1-carboxylic acid (1), but to a mixture of cis- and trans-2-benzylcyclopentane-1-carboxylic acid (6a and 7a) contrary to the description in literature. Unsaturated acid (1) was obtained as a major product by the Wolff-Kishner-Huang-Minlon reduction of 2a accompanied with 1-carboxy-6-phenylbicyclo[3.1.0]hexane (8). The reduction of 2a with zinc dust in acetic acid and the reduction of the methyl ester (2b) by way of its thioketal were also investigated.