Synthesis of Enantiopure Homoallylic Alcohols and Ethers by Diastereoselective Allylation of Aldehydes

Enantiopure homoallylic alcohols 5, which are important building blocks in organic synthesis, are obtained with an ee of greater than 99% and a yield of 75–95% by cleavage of the secondary homoallylic ethers 4 using sodium in liquid ammonia. The ethers 4 are formed with excellent diastereoselectivity and in 52–89% yield by treatment of the aldehydes 1 with the trimethylsilyl ether of N‐trifluoroacetylnorpseudoephedrine (2) in the presence of a catalytic amount of TMS triflate or TMS borontriflate, followed by addition of allylsilane 3. Nearly all achiral aliphatic aldehydes employed gave a diastereoselectivity of over 99:1. With the chiral aldehydes 24, the difference between matched and mismatched pairs was low; this reveals that there is strong reagent control. One of the most selective syntheses of enantiopure homoallylic alcohols 4 is achieved by allylating aldehydes 1 with allylsilane 3in the presence of the norpseudoephedrine derivative 2 and catalytic amounts of TMSOTf, followed by reductive cleavage. With achiral aliphatic aldehydes the enantiomeric excess of 4 was over 99%. With chiral aldehydes excellent reagent control was observed even for the mismatched pairs.