Enantio- and diastereoselective protonation of photodienols: Total synthesis of (R)-(-)-lavandulol

Article abstract of DOI:10.1021/jo00129a030

The total synthesis of (R)-(-)-lavandulol 1 has been achieved by asymmetric protonation of photodienols obtained from the irradiation of prochiral α,β-unsaturated esters. The photodeconjugation of ethyl 5-methyl-2-(1'-methylethylidene)-4-hexenoate (3a), carried out in the presence of catalytic amounts of a β-amino alcohol prepared from (±)-camphor, gives the β,γ-unsaturated isomer 2a in good yields but with moderate enantioselectivities (40% ee). In contrast, irradiation of the corresponding ester 3b, bearing the 1,2:5,6-di-O-isopropylidene-D-glucose group as a chiral alkoxy moiety, affords the deconjugated product 2b in high de (> 95%). Simple reduction of the ester function with LiAlH₄ gives (R)-(-)-lavandulol (1) without loss of optical purity.