Search

The stereochemical outcome of the reaction is opposite to that of the corresponding reaction of (I) and (II) using a palladium catalyst which selectively produces (E)-isomers.

2-Methyl-3,4-dihydro-1 H-2-benzoselenopyranium salt (1) was reduced by some metallic reagents or magnesium metal via the single-electron transfer (SET) process to give 2-[2-(methylseleno)ethyl]-toluene (2). Magnesium metal was a good SET reducing agent. Some other selenonium or sulphonium salts (7), (14). (22), (27) and (32) were similarly reduced by magnesium. Particularly, sonication accelerated the reductions. Iµ-Eneselenonium salt (43) was treated with activated magnesium to give a cyclised pyrrolidine derivative (44).

Medium-sized sulfur- or selenium-containing heterocyclic compounds were synthesized by the reductive cross-piece bond cleavage of bicyclic sulfonium and selenonium salts bearing a bridgehead sulfur or selenium atom with magnesium metal or sodium borohydride.

9-Benzyl-10-aza-9-thiaphenanthrenes ( 3 ) generated from 9-benzyl-10-aza-9-thiaphenanthreniun salts ( 2 ) by treatment with base underwent thermal 1,2-benzyl migration to give the corresponding 6-benzyl-6H-dibenzo[c,e][1,2]thiazines ( 4 ).

Tris(methylseleno)- and tris(phenylseleno)boranes added to acetylenes to afford methylseleno- and phenylseleno-substituted Z -vinylselenides in high yields. The addition reactions proceeded by way of free radicals and were applied to cyclization reactions of enyne compounds. The radical cyclization provided pyrrolidine derivatives diastereoselectively.

The anion (2) generated from 9-methyl-10-aza-9-thiaphenanthrene (1) reacted with carboxylic ester to give the spiro compounds (9a), (9b) via Sommelet-Hauser rearrangement, whose structures have been confirmed by an X-ray crystal structure determination of (9a).

1-Benzothiopyranylium salts 1 underwent polar cycloaddition with conjugated dienes 2 to give benzo-fused bicyclic sulfonium salts 3 having sulfur at a bridgehead position in good yields, which were easily transformed into spiro compounds 4 and 5 by treatment with base.

On treatment with tellurium tetrachloride in dichloromethane at room temperature, acetals and thioacetals are easily cleaved to regenerate original carbonyl compounds in good yields

2-Thianaphthylium ions (1) underwent a polar cycloaddition with 1,3-dienes to afford benzo-fused bicyclic sulfonium salts (2) bearing sulfur atom at bridge-head in excellent yields. The cycloadducts underwent retro-addition reaction to generate the cation (1), which was easily trapped with other diene. Reaction of the adduct (2d) with several nucleophiles caused the ring-opening of (2d) to afford 1-allyl (6) and 1-homoallyl substituted 2-thiochromenes (7) in good yields.

Various Se,O-heteroacetals were prepared by the LiAlH 4 reduction of diselenides 1 followed by alkylation with methoxymethyl chloride or (2-methoxyethoxy)methyl (MEM) chloride. Olefinic and acetylenic α-seleno carbenium ions were generated by the selective C-O bond cleavage of O-(2-methoxyethyl)-Se,O-heteroacetals with titanium(IV) chloride end cyclized to give the seleno heterocyclic compounds. Olefinic MEM-selenides 3a,b,d-f,h underwent the endo-mode cyclization to afford 4-chloroselenacycloalkanes 4a,b,d-f,h in good yields, wherein acetylenic MEM-selenides 12b-e,g-) underwent the exo-mode cyclization to give 3-(1-chloroalkylidene)selenacycloalkanes 13b-e,g-j. This new utilization of α-seleno carbenium ions was also applied to the intramolecular and intermolecular Friedel-Crafts reactions

Reaction of 3,7-dimethyl-6-methylthio-2-oxopurine (1) with Grignard reagents or organolithiums afforded 8-adducts (2), whereas the corresponding reaction of 3,7-dimethyl-2-oxopurine (6) gave 6-adducts (7). The adducts (2) and (7) were converted into 8-substituted theobromines (4) and 6-substituted 3,7-dimethyl-2-oxopurines (8), respectively. 8-Chlorotheobromine (5) reacted with Grignard reagents in the presence of a catalytic amount of NiBr 2 (PPh 3 ) 2 to give (4) in good yields

Oxacyclooctyl (oxocanyl) carbenium ions generated by treatment of O-(5-hexenyl)-Se,O-heteroacetals or O,O-acetals with SnCl4 underwent intramolecular 1,5-hydride transfer, and the α-oxy carbenium ions newly formed were hydrolyzed to give the 7-oxohexanols or 7-oxohexyl chlorides in good yields. Various O-(5-hexenyl)-Se,O-heteroacetals or O,O-acetals were converted into 7-oxohexanols or 7-oxohexyl chlorides.

The conjugated (Z)-enynes 2a, 2d–g and (Z)-enediynes 2h–j were synthesized by dehydration of prop-2-ynyl alcohols 1a, 1d–j with polyphosphoric acid trimethysilyl ester.

3, 6-Dihydro-2H-selenopyrans 2 with an electron-withdrawing group at the 2-position were prepared by the Diels-Alder reaction of butadienes with selenoaldehydes generated in situ from selenocyanates 1 and triethylamine. Oxidation of the dihydroselenopyrans 2 with 1.5 eq of m-chloroperbenzoic acid provided 2H-selenopyrans 9 and 3, 6-dihydro-2H-selenopyran-2-yl m-chlorobenzoates 10. The benzoates 10 were smoothly converted into the selenopyrans 9 using polyphosphoric acid trimethylsilyl ester. The selenopyrans 9 were methylated with methyl trifluoromethanesulfonate to give Se-methyl selenopyranium trifluoromethanesulfonates 12. Deprotonation of the selenonium salts 12 with sodium hydride or triethylamine generated the selenabenzene derivatives 13, but they were too unstable to be isolated. Therefore, we confirmed the generation of 13 by 1H- and 13C-NMR spectroscopy at -30°C.

Reaction of thiazolo[3,2- b ][1,2,4]triazolium N -phenacylides 3 with dimethyl acetylene-dicarboxylate gave novel compounds, 2-(1 H -pyrrolo[2,1- c ]-1,2,4-triazolyl)ethenyl thiobenzoates 4 and 2-[2-(1 H -pyrrolo[2,1- c ]-1,2,4-triazolyl)ethenylthio]propenoates 5 . The former products 4 would be formed via a new type of intramolecular benzoyl migration of the intermediary 1:1 adducts 6 .

Reactions of 9-substituted 9-thia-10-azaphenanthrenes with several electrophiles have been investigated. Reaction of 9-alkyl-9-thia-10-azaphenanthrenes with dimethyl acetylenedicarboxylate (DMAD) afforded dibenzothiazonine derivatives 4 and 5, dibenzothiazocine derivatives 6, 2-alkylsulfinyl-2′-vinylaminobiphenyls 7, and bis(biphenylylimino)ethane derivatives 8. The product distribution was markedly influenced by the substituent on the sulfur atom. 9-Methyl 3a and 9-isopropyl derivatives 3d afforded predominantly dibenzothiazonine derivatives 5a and 4d, respectively, while 9-ethyl 3b, 9-isopropyl 3c and 9-cyclohexyl derivatives 3e gave predominantly dibenzothiazocine derivatives 6 and alkylsulfinyl vinylaminobiphenyls 7. In contrast, the reactions of 9-phenyl-3f or 9-vinyl-9-thia-10-azaphenanthrene 3g with DMAD afforded only the corresponding dibenzothiazocine derivative 6. Reactions of 9-alkylthiaazaphenanthrenes 3a–c with methyl propiolate (MP) in benzene afforded dibenzothiazecine derivatives 12 as 1:2 adducts. Reactions of compounds 3a–c with diphenylcyclopropenone in ethanol yielded the ring-opened products 13, while the same reaction in benzene solvent afforded the 4-quinolone derivatives 14via intramolecular cyclization of a ketene intermediate, L.

Benzothiazinone (1) was chlorinated with N-chlorosuccinimide and sub- sequently submitted to [2+4] cycloaddition with 1,3-dienes in the presence of silver perchlorate to afford cyclic sulfonium salts (3). Reactions of (3) with sodium borohydride or sodium hydride provided 4-vinyltetrahydro-3,6-epithiobenzazocine derivatives (9) in good yields

2-Benzothiopyrylium salts 4 and 6 underwent polar cycloaddition with conjugated dienes to afford benzo-fused bicyclic sulfonium salts 7 and 8, respectively, having sulfur at a bridgehead position, in good yields. The salt 4 bearing an electron-withdrawing group at the 3-position was much more reactive than was the salt 6. The structures of the cycloadducts have been established by X-ray crystallography of compound 7a, indicating a cis-fused configuration. In contrast, attempted reaction of the salt 4 with furan as a heterocyclic diene resulted in the electrophilic substitution of the furan by the salt, giving compound 9. The cycloadducts 7 underwent retro-addition to generate 2-benzothiopyrylium ion 4, which was easily trapped with other dienes or active methyl compounds to give the corresponding adduct 7 or 1-alkylated 1H-2-benzothiopyran 5, respectively. Reactions of the cycloadducts 7 with a variety of nucleophiles caused ring opening to afford 1-allyl-12 and 1-homoallyl-substituted 1H-2-benzothiopyrans 13 in good yields. On the other hand, the cycloadduct 8, when treated with nucleophiles, underwent a novel ring transformation along with nucleophilic ring-opening.

Generation of α-lithio-Se, O-heteroacetals was accomplished by direct deprotonation of O-methoxyethylselenoacetals with lithium 2, 2, 6, 6-tetramethylpiperidide. Alkylation of the α-lithioheteroacetals smoothly proceeded to give the products 6 and 7. Olefinic Se, O-heteroacetals 6c and 6d were cyclized via α-seleno carbenium ions generated by selective C-O bond cleavage with titanium tetrachloride to provide the cyclohexane derivatives 8a and 8b, respectively.

A novel cyclic sulfilimine, 2-methyl-2,4,1-benzodithiazin-2-ium-1-ide (4) was synthesized by deprotonation of the corresponding azasulfonium salt (3) with base. The compound 4 was oxidized with potassium permanganate to afford the sulfoximine 5, exclusively. On refluxing in several solvents, compound 4 underwent a ring contraction to afford benzothiazole (8) via the 1,2-imino shift. The reaction of 4 with a variety of electrophiles, such as dialkyl acetylenedicarboxylate, acylating agents, diphenylcyclopropenone, and phenyl isocyanate, afforded ringopened adducts. Synthetic approaches to cyclic disulfonium ylides are also described.

γ-Chalcogen-substituted prop-2-ynyl cations are generated by the reactions of diethyl acetals 1 and 2 with BF3–Et2O and react with various mild nucleophiles without isomerisation to allenyl cations to afford the prop-2-ynylated products 3a–e and 5a–c in good yields.

Ring transformation of the adducts 1 of the polar cycloadditions of 2-benzothiopyrylium salts induced by a variety of bases and reducing agents has been investigated. Treatment of the 9-unsubstituted cycloadducts 1a, b, c with strong bases such as lithium diisopropylamide (LDA), sodium hydride and potassium carbonate afforded the vinylcyclopropane derivatives 2 and the 1,5-methano-2-benzothionines 3. In contrast, treatment of compound 1a with weak bases such as triethylamine, diethylamine and potassium acetate gave no compounds 2a or 3a, but only ring-opened compounds 4a in high yields via SN2-type processes. In these reactions, weak bases acted as nucleophiles. In contrast, the 9-benzoyl cycloadduct 1d reacted with both weak and strong bases to afford, mainly, the similar ring-transformed product 2d. Whilst the strong base LDA gave compound 3d(as a minor product) in addition to compound 2d, weak bases such as diethylamine and butylamine also acted as nucleophiles to give the corresponding ring-opened compounds 4d as minor products. A mechanistic interpretation of the above reactions is presented. When heated at high temperature, the vinylcyclopropane 2d was converted into the cyclopentene derivative 5. Ring transformations of compounds 1 with reducing agents such as sodium borohydride and samarium diiodide are also described.

Treatment of 2-vinylcyclopropyl sulfoxides lacking an α-hydrogen with acid anhydrides produced butadienylthionium ion intermediates to give cyclic or acyclic conjugated dienes.

α-Lithio conjugated enyne sulfones, easily generated from enyne sulfones 1 and 2 and MeLi, upon reaction with carbonyl compounds followed by treatment with MeLi afford the 2,4-diynols 4a–g and 5a–c in high yields.

Reactions of thiazolium and benzothiazolium N-phenacylides with dimethyl acetylenedicarboxylate (DMAD) have been reexamined. The thiazolium N-phenacylides 5, generated in situ from 4-methyl- or 5-phenyl-3-phenacylthiazolium bromides 13 with triethylamine, reacted with DMAD in dry DMF to give the thiazole ring-opened products 15, in which two molecules of DMAD had been incorporated. The reactions when conducted in both aqueous DMF and in dry DMF in the presence of lithium perchlorate gave the hemithioacetals 6 which could be transformed into the 1 : 2 reaction products 15 of the ylides and DMAD. Benzothiazolium N-phenacylides 8 similarly reacted with DMAD to afford the 1 : 2 reaction products 19 or the hemithioacetals 20. The reaction mechanism is discussed.

2-Benzothiopyrylium salt 1 reacted via a [4++ 2]-type polar cycloaddition with dienes 2 in the presence of methanol to afford benzo-fused bicyclo[2.2.2] compounds 5, while in the absence of methanol cycloaddition of 1 with 2,3-dimethylbuta-1,3-diene 2a afforded a novel benzo-fused tricyclic compound 4a, whose structure has been confirmed by X-ray crystallography.

(Z)-5-(Phenylselenomethylene)pyrrol-2-ones 18–22 have been obtained in good yields from the cyclization of ω-seleno-substituted alkynyl amides 11–15 with ButOK–18-crown-6.

Deprotonation of 2-alkyl-3-benzoyl-2-thiochromenium salts 1 or 2 with 2 equiv. of triethylamine in ethanol affords the unexpected benzothiopyran derivatives 3 and 4; the structure of 3a is confirmed by X-ray crystallography.

2-Ethoxy-4-(phenylchalcogeno)but-3-ynyl ketones 1-10 were reduced with LiBH(4) in Et(2)O diastereoselectively to give 5-(phenylchalcogeno)pent-4-yn-1-ols 11-20. Treatment of the phenylchalcogen-substituted alkynyl alcohols 11-20 with t-BuOK in t-BuOH provided useful (Z)-2-((phenylchalcogeno)methylene)tetrahydrofurans 21-31 stereoselectively.

Treatment of 9-thiaphenanthrenium salt 1 with conjugated dienes underwent regio- and stereospecific [2++4]-type polar cycloaddition to afford the corresponding sulfonium salt adducts 2 in good yields. Nucleophilic attack of some alcohols to the cycloadduct 2a led to the two kinds of ring-opened compounds 3 and 4. Reactions of compound 2a with a variety of bases yielded the vinylcyclopropane derivative 5 and the ring-opened product 6. Treatment of compound 2a with LDA in the presence of methyl acrylate afforded the compound 7 which is believed to derive from Michael-addition of a reactive ylide intermediate to an α,β-unsaturated ester. Reductive cleavage of compound 2a with NaBH4 or SmI2 afforded the ring-opened product 8.

Generation of butadienylthionium ions in the Pummerer reactions of 2-vinylcyclopropyl sulfoxides has been investigated. Although the Pummerer reactions of 2-vinylcyclopropyl sulfoxides 1 are complicated, benzothiazinone derivatives 10 smoothly react with trifluoroacetic anhydride to give 1,3-dienes in good yields. The reactions proceed via butadienylthionium ions by proton abstraction from the 2′-methyl group or the cyclopropane ring. Reactions of disubstituted benzothiazinones 10e–h provided cyclic dienes while treatment of mono- or un-substituted derivatives gave acyclic conjugated dienes 11a–d. 2-Vinylcyclopropyl sulfoxides 1 and 10 were prepared by MCPBA oxidation of the corresponding 2-vinylcyclopropyl sulfides 19 and 23, respectively, which were obtained by cyclopropanation of α-chloro sulfides with 1,3-dienes via the 5,6-dihydro-2H-thiopyranium intermediate 22.

2'-Vinyl-2H-1, 4-benzothiazin-3(4H)-one-2-spirocyclopropanes (1) were irradiated with a tungsten lamp at room temperature in the presence of a catalytic amount of diphenyl dichalcogenide to provide 1, 2-dioxolane derivatives (3) in good yields. Diphenyl diselenide was more effective than diphenyl disulfide as a radical source. The photochemical [3+2] cycloaddition of 1b with electron-deficient alkenes proceeded smoothly under reflux in benzene to give spiro-cyclopentanes (5). Spiro-cyclopentenes (6) were formed by the photochemical [3+2] cycloaddition of 1b with alkynes.

Dibenzo[c,e][1,2]thiazinylium tetrafluoroborate underwent polar cycloaddition with several 1,3-butadienes to afford new sulfur-nitrogen-containing sulfonium heterocycles in good yields. The cycloaddition with unsymmetrical 1,3-butadiene, isoprene afforded two regioisomeric adducts. Deprotonation of the cycloadduct underwent ring transformation to yield a pyrrole derivative.

Deprotonation of the cycloadducts, which were newly obtained from polar cycloaddition of monocyclic 1,2-thiazinylium salt with 1,3-butadienes, with a strong base provided 1,2-azathiabenzenes having sulfur at a bridgehead position.