Complementary reduction conditions have been identified that provide ready access to each respective diastereomer of bi- and tricyclic, trisustituted gamma-lactones starting from the corresponding cyclic gamma-keto acids. Subjection of cyclic gamma-keto acids to silane reagents in the presence of trifluoroacetic acid provides all syn-gamma-lactones, while reduction with trialkylborohydrides furnishes the syn,anti-gamma-lactones. The conditions are mild and provide the product lactones in good yields and modest to excellent selectivity.
Acids: Efficient Access to Trisubstituted γ-Lactones. -The title reactions are developed to afford each diastereomer of the title compounds. Conditions A) which use a trialkylborohydride afford the syn/anti lactones as the major products. Conditions B) which include a silane reagent and TFA give mainly the all syn products. -(BERCOT, E. A.; KINDRACHUK, D. E.; ROVIS*, T.; Org. Lett. 7 (2005) 1, 107-110; Dep. Chem., Colo. State Univ., Fort Collins, CO 80523, USA; Eng.) -Steudel 17-114
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