Masahito Segi

An efficient construction of a selenocarbonyl unit by the reaction of acetal derivatives with bis(dimethylaluminum) selenide

Abstract The construction of a carbon-selenium double bond was achieved by the reaction of acetal derivatives with bis(dimethylaluminum) selenide, and a variety of selenocarbonyl compounds containing selenoaldehydes, selenoformamides, and selenonesters were efficiently synthesized.

Novel route to selenoketones from ketones by the use of bis(dimethylaluminum) selenide

Abstract Bis(dimethylaluminum) selenide, prepared in situ via transmetallation reaction of bis(trimethylsilyl) selenide with dimethylaluminum chloride, reacted with ketones in the presence of a diene to give Diels-Alder adducts of the corresponding selenoketones and the diene.

α,β-Unsaturated selenoaldehydes and selenoketones the reaction behavior as a heterodiene and/or a dienophile

Abstract α,β-Unsaturated selenoaldehydes and selenoketones, generated in situ by selenation of the corresponding carbonyl compounds with bis[dimethylaluminum) selenide, underwent regioselective self-condensation to yield cyclic diselenide derivatives. On the other hand, in the presence of a trapping agent, they underwent intermolecular Diels-Alder cycloadditions in two different modes depending on the trapping agent, that is, as a heterodiene toward norbornadiene or a dienophile toward cyclopentadiene. FS

Intramolecular Diels-Alder reaction of selenoaldehydes

Abstract Intramolecular Dieis-Alder reaction of selenoaldehydes which were generated from bis(trimethylsilyl) selenide and dienals gave the corresponding bicyclic adducts.

Diastereoselective aldol condensation of acylsilane silyl enol ethers with acetals

Abstract Treatment of E - or Z -acylsilane silyl enol ethers derived from acylsilanes having an enolizable methylene proton with a mixture of aromatic aldehyde dimethyl acetals and TiCl 4 in dichloromethane gives the corresponding 2,3- anti -3-methoxyacylsilanes in high d.e., independent of the geometry of double bond in acylsilane silyl enol ethers. On the other hand, E -acylsilane silyl enol ethers react with acetals of aliphatic aldehydes to afford the corresponding aldol adducts with syn -selectivity, while the reaction of Z -isomers provides the products with anti -selectivity.

The reaction of selenoaldehydes with 2-methoxyfuran using their generation by retro Diels–Alder reaction

Abstract Selenoaldehydes, regenerated by thermal retro Diels–Alder reaction of anthracene cycloadducts under neutral conditions, reacted with 2-methoxyfuran to give methyl penta-2,4-dienoates along with the deposition of elemental selenium. In a similar reaction with 2-methoxyfuran using thioaldehyde, thiirane compound was isolated. This suggests the formation of selenirane intermediates in the above reaction.

A Useful Method for the Synthesis of Selenoaldehydes with Electron-withdrawing Substituents

Abstract Several selenoaldehydes substituted with electron-withdrawing groups were synthesized by the reaction of the corresponding gem-dichlorides with selenium dianion, generated by the treatment of bis(tributyltin) selenide and tetrabutylammonium fluoride trihydrate, and were in situ trapped by 1,3-dienes to give Diels-Alder adducts.

Ring-enlargement of cyclopropylacylsilanes with sulfuric or triflic acid. Selective formation of cyclobutanones or 2-silyl-4,5-dihydrofurans

Abstract Reaction of cyclopropylacylsilanes with sulfuric or triflic acid in aprotic solvent affords the corresponding cyclobutanone or 2-silyl-4,5-dihydrofuran derivatives, depending upon the substituents on the three-membered ring or acid used. The use of triflic acid results in the selective formation of the dihydrofurans.

Reaction of acylsilanes with sulfur ylides. selective formation of silyl enol ethers or β-ketosilanes.

Abstract The reaction of acylsilanes with sulfur ylides in THF results in the formation of the corresponding silyl enol ethers or β-ketosilanes. The relative ratio of these products varies with the ylide conditions and the stability of ylide used. It is noteworthy that silyl enol ethers were formed under the salt-free ylide conditions, and that β-ketosilanes were yielded in the presence of soluble inorganic salts in THF, selectively. The formation of both products would be interpreted in terms of the anionotropic and cationotropic rearrangements of silyl group in the reaction intermediate.

Intramolecular Diels-Alder Reaction of Thioaldehydes

Abstract Intramolecular Diels-Alder reaction of thioaldehydes which were generated from bis(trimethylsilyl) sulfide and dienals gave the corresponding bicyclic adducts.