Synthesis of α,β-Unsaturated Aldehydes by 1,3-Carbonyl Transposition through One Carbon Homologation. Part 2

Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta-700 082

The easily accessible 2-(diethoxymethyl)-6-methoxy-1-tetralone (1) on condensa­tion with methylmagnesium iodide and benzylmagnesium chloride followed by treatment with BF₃.Et₂O affords 6-methoxy-1-methyl-3,4-dihydro-2-naphthaldehyde (2) and 1-benzyl-6-methoxy-3,4-dihydro-2-naphthaldehyde (3), respectively. The carbinols derived from the reaction of 2-(diethoxymethyl)-1-indanones (4a-4c) with methyllithium undergo smooth transformations to the respective 3-methyl-1H-indene-2-aldehydes (5a-5c). endo-2-(p-Methoxyphenyl)-5-methylbicyclo[3.2.1]octan-6-en-7-aldehyde (14) has been prepared from endo-2-(p-methoxyphenyl)-5-methylbicyclo[3.2.1]octan-6-one (12) through the respective diethoxymethyl derivative (12) by sodium borohydride reduc­tion followed by acid-catalysed rearrangement of the resulting diacetal carbinol.