Improved preparation of angelate esters

The First Entry to Complex Bakkanes: A Highly Effective Retroaldol–Aldol-Based Approach to (−)-Bakkenolides III, B, C, and H

“…The hydroxyl groups in bakkenolide III are clearly in different steric environments and this was expected to translate into regioselective acylations. Bakkenolide III in the presence of the Yamaguchi mixed anhydride derived from angelic acid and under conditions earlier found to avoid the facile angelic→tiglic isomerization16 formed (−)‐bakkenolide C ( 2 )1d in 86 % yield without detectable amounts of C9‐acylated material or tiglic ester (Scheme ). The bakkenolide C so obtained was identical with a sample secured by partial hydrolysis1b,1d,1f of natural bakkenolide B.…”

A Route to the Thapsigargins from (S)‐Carvone Providing a Substrate‐Controlled Total Synthesis of Trilobolide, Nortrilobolide, and Thapsivillosin F

“…To distinguish the five hydroxyl groups in the molecule, the endgame strategy had been designed to minimize protecting group manipulation and take advantage of the inherent order of reactivity of the alcohols in a concise fashion. Accordingly, the C3 hydroxy group was first esterified with angelic acid under Yamaguchi conditions [19] to provide 29 before unmasking the tertiary alcohols with TBAF to yield 30. Selective acylation of the C10 hydroxy group was then achieved with isopropenyl acetate mediated by polymer-supported tosic acid.…”

Enantioselective Total Synthesis of the Highly Oxygenated 1,10‐seco‐Eudesmanolides Eriolanin and Eriolangin

“…In addition, an X‐ray diffraction analysis of our synthetic product 1 provided a further independent proof of the absolute configuration by anomalous X‐ray scattering 38. Using a modified Yamaguchi esterification,39 31 could also be transformed smoothly to angelate 33 without Z / E isomerization. Deblocking to give 2 delivered (−)‐eriolangin, which also turned out to be identical to the natural product by comparison of optical rotation data 40…”