In tandem reactions, cyclopropylcarbinols are obtained from allyloxylithium or -magnesium intermediates, generated in situ by alkylation of conjugated aldehydes, ketones, and esters as well as from allyl carboxylates or vinyloxiranes. Using this methodology, numerous fragrance ingredients and their precursors were efficiently converted to the corresponding cyclopropylcarbinols.
A new synthesis of α-santalol (1) is described. 1-Benzyloxy-4-bromo-2-methyl-2-butene (6) was converted by the reaction with nickel carbonyl to the π-allylic nickel bromide complex (7), which reacted with (−)-π-bromotricyclene (8) to afford benzyl ether (2). The benzyl ether (2) was led to (1) (cis: trans=40: 60) by reductive cleavage of the benzyloxy group.