Divergent Asymmetric Total Synthesis of All Four Pestalotin Diastereomers from (R)-Glycidol

All four chiral pestalotin diastereomers were synthesized in a straightforward and divergent manner from common (R)-glycidol. Catalytic asymmetric Mukaiyama aldol reactions of readily-available bis(TMSO)diene (Chan’s diene) with (S)-2-benzyloxyhexanal derived from (R)-glycidol produced a syn-aldol adduct with high diastereoselectivity and enantioselectivity using a Ti(iOPr)₄/(S)-BINOL/LiCl catalyst. Diastereoselective Mukaiyama aldol reactions mediated by catalytic achiral Lewis acids directly produced not only a (1′S,6S)-pyrone precursor via the syn-aldol adduct using TiCl₄, but also (1′S,6R)-pyrone precursor via the antialdol adduct using ZrCl₄, in a stereocomplementary manner. A Hetero-Diels-Alder reaction of similarly available mono(TMSO)diene (Brassard’s diene) with (S)-2-benzyloxyhexanal produced the (1′S,6S)-pyrone precursor promoted by Eu(fod)₃ and the (1′S,6R)-pyrone precursor Et₂AlCl. Debenzylation of the (1′S,6S)-precursor and the (1′S,6R)-precursor furnished natural (−)-pestalotin (99% ee, 7 steps) and unnatural (+)-epipestalotin (99% ee, 7 steps), respectively. Mitsunobu inversions of the obtained (−)-pestalotin and (+)-epipestalotin successfully produced the unnatural (+)-pestalotin (99% ee, 9 steps) and (−)-epipestalotin (99% ee, 9 steps), respectively, in a divergent manner. All four of the obtained chiral pestalotin diastereomers possessed high chemical and optical purities (optical rotations, ¹H-NMR, ¹³C-NMR, and HPLC measurements).

The first total synthesis of (-)-solanapyrone E based on domino Michael strategy

[figure: see text] A phytotoxin, solanapyrone E, has been synthesized from the decalone prepared by the domino Michael reaction of the kinetic enolate of optically pure acetylcyclohexene with methyl crotonate. After several transformations on the decalone ring, condensation of a methyl acetoacetate equivalent installed a pyrone moiety and introduction of a hydroxymethyl unit into the pyrone ring furnished solanapyrone E.