Meyersのアルデヒド合成 : ジヒドロ-1, 3-オキサジンを経由する合成

概要

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A technique is described for the preparation of aldehydes based upon the dihydro-1, 3-oxazine ring system. 2, 4, 4, 6-Tetramethyl- (1a) or 2-benzyl-4, 4, 6-trimethyl-5, 6-dihydro-1, 3-oxazine (1b) can be smoothly con-verted into the lithio salts on treatment with organolithium reagents in THF at -78°. The lithio salts are excellent nucleophiles and react with alkyl halides or carbonyl compounds to give elaborated oxazines. The crude oxazines are reduced with sodium borohydride at pH 7 in a THF-EtOH-H<SUB>2</SUB>O mixture at -40° to give the tetrahydro-1, 3-oxazines (2), which on hydrolysis with aqueous oxalic acid give the aldehydes. No purification of the intermediates is necessary, and the aldehydes are isolated simply by steam distillation or extraction with organic solvents after hydrolysis. Thus, substituted acetaldehydes and α, β -unsaturated aldehydes are obtained in overall yields of 4574%. Reduction of (2) with sodium borodeuteride gives C-1 deuterated aldehydes. Modification of the method affords a variety of functionalized aldehydes and aldehyde derivatives, and further enables the introduction of CHO groups into compounds with complex structures.
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