Preparation and Reactions of Diorganozincs from Dienic Silyl Enol Ethers

Article abstract of DOI:10.1021/jo00116a013

The hydroboration of the dienic silyl enol ethers 1a-d with Et2BH produces organoboranes which are readily converted under mild conditions by a treatment with Et2Zn to the corresponding dialkylzincs 2a-d.These organometallics react after transmetallation with CuCN*2LiCl with various electrophiles affording polyfunctional silyl enol ethers of type 4.In the presence of the chiral catalyst (1R,2R)-bis(trifluoromethanesulfonamido)cyclohexane 6, the dialkylzinc 2b was added to various aldehydes leading to hydroxy silyl enol ethers of type 8 in satisfactory yields (45-77percent) and excellent enantioselectivities (85 to >96percent ee).The chiral products 8 can be oxidatively cyclized using t-BuOOH and catalytic amounts of VO(acac)2 furnishing trisubstituted tetrahydopyrans like 9a,b with high diastereoselectivity.An iodoalkoxylation of 8a affords after HI elimination and Jones oxidation the unsaturated valerolactone 13.