Preparation of Some 9-Hydroxy-2-oxaspiro[4.5]dec-8-ene-1,7-dione Derivatives by Reductive Alkylation of 3,5-Dimethoxybenzoic Acid With 1,2-Dihaloalkane and Oxiran Electrophiles

Lithium in liquid ammonia mediated reductive alkylation of 3,5-dimethoxybenzoic acid (3) with 1,2-dibromoethane, or 1-bromo-2-chloroethane, followed by acid hydrolysis, afforded 9-hydroxy-2-oxaspiro[4.5]dec-8-ene-1,7-dione (1a). Reductive alkylation of (3) with unbranched 1,2-dibromoaikanes (5b-g), 1,2-dibromo-3-methylbutane and 1,2-dibromo-3,3-dimethylbutane gave 3-alkyl-9-hydroxy-2-oxaspiro[4.5]dec-8-ene-1,7-dione derivatives (1b-i) in moderate yields with the exception of (1i). The major product of the last reaction was 1-(2-bromo-3,3- dimethylbutyl )-3-hydroxy-5-oxocyclohex-3-ene-1-carboxylic acid (9). No reductive alkylation of (3) was observed with 2,3-dibromobutane or 1,2-dibromo-2methylpropane. Reductive alkylation of (3) with the oxiran derivatives (8a-d) afforded the 2-oxaspiro[4.5]dec-8-ene-1,7- dione derivatives (1a-c,j). Reductive alkylation of (3) with 1,3-dibromopropane and l-bromo-3-chloropropane gave, after hydrolysis, 1-(3-bromopropyl)-3-hydroxy-5-oxocyclohex-3-ene-l- carboxylic acid (12a) and 1-(3-chloropropyl)-3-hydroxy-5-oxocyclohex-3-ene-1-carboxylic acid (12b). The conversion of (1a) into 8-[1-( ethoxyimino )butyl]-9-hydroxy-2-oxaspiro[4.5]dec-8-ene-1,7-dione (2a) is described.