syn ‐Diastereoselective Homoaldol Reactions: γ‐Hydroxyalkylation of ( Z )‐2‐Butenyl Carbamates and Synthesis of β,γ‐ cis ‐Di‐ and ‐Trisubstituted γ‐Lactones

The preparation of the syn ‐homoaldol derivatives syn ‐3 in ≥ 85% stereoselectivity is achieved by reaction of the lithiated ( Z )‐2‐butenylcarbamate 1 , X OC(O)N( i Pr) 2 , M Li, with aldehydes or ketones. Previously, only access to anti ‐diastereomers was possible. Mercury( II )acetate‐catalyzed methanolysis of syn ‐ 3 furnishes a cis ‐γ‐lactol methyl ether: the relative configurations at C‐3 and C‐4 are retained. Subsequent oxidation leads to lactones, e.g. to (±)‐quercus‐lactone b.