Facile Chemo-, Regio-, and Diastereoselective Approach to <i>cis</i>-3,5-Disubstituted γ-Butyrolactones and Fused γ-Butyrolactones

Chemoselective SN2‘ condensation of primary enolates of alkyl methyl ketones 2a−e with dimethyl bromomethylfumarate (1) followed by highly diastereoselective NaBH4 reduction of the ketone function in the formed ketodiesters 3a−e and the regioselective in situ lactonization of the unisolable intermediates 4a−e exclusively furnished the cis-3,5-disubstituted γ-butyrolactones (±)-5a−e in very good yields. Similarly, the face-selective coupling reaction of cyclohexanone enolate with 1 to form a mixture of diastereomers in an 8:2 ratio followed by a highly selective reductive cyclization of 9 plus 10 exclusively provided the cis-octahydrobenzofuran (±)-12 in 70% overall yield.