Cyclic hydroboration of an appropriately substituted 1.5~diene yields a 1,5 dial as the major product which can be converted to the racemic
Prelog-Djerassi lactone. The widespread occurrence of the three carbon unit 1 in natural products of current synthetic interest has prompted us to investigate methodology for the stereocontrolled construction of intermediates of this type. We are particularly interested in substances appropriately substituted at R' and R2 to allow for transfer of stereochemical information present in l_ to distal prochial centers on the acyclic carbon chains R' and R2. Diols such as 1 in principal meet this requirement and we have recently observed the stereocontrolled synthesis of 2a via a cyclic hydroboration routels2 described below. --Subsequent transformations provided a structure proof for this substance and a practical illustration of the method for the preparation of the Prelog-Djerassi lactone J3 and its C-6 epimer.4 The requisite diene was constructed in a highly stereoselective fashion using Still's sigmatropic rearrangement route to Z-trisubstituted olefins. 5 Aldehyde T6 was treated with P-propenylmagnesium bromide in THF to yield the alcohols 5 (BB%).7 Conversion of 5 to 6was accomplished through a one-pot sequence (l-KH, THF 0'; 2-ICH2SnBu3, THF; 3-n-Buli, THF, -78') in 75% yield7 after removal of a small amount of the E-diene by flash chromatography.8 The isomeric purity of cwas shown to be greater than 99.5% by VPC,omparison' of the derived acetate with a sample of the E-acetate prepared by Johnson's method.