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Total Syntheses of the Gregatins A–D and Aspertetronin A: Structure Revisions of These Compounds and of Aspertetronin B, Together with Plausible Structure Revisions of Gregatin E, Cyclogregatin, Graminin A, the Penicilliols A and B, and the Huaspenones A and B
Author(s) -
BurghartStoll Heike,
Brückner Reinhard
Publication year - 2012
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201200207
Subject(s) - stereocenter , chemistry , stereochemistry , total synthesis , acylation , absolute configuration , carbon atom , enantioselective synthesis , ring (chemistry) , organic chemistry , catalysis
Comprehensive comparisons of 1 H and 13 C NMR chemical shift values in the furanone cores a , b , and c provide plausible support for a reassessment of the furanone nuclei of the title compounds from b to c . Total syntheses via enantiomerically pure lactic esters were based on the Seebach–Fráter “self‐reproduction of stereocenters” methodology. Attachment of the hexadienyl side‐chain in a trans , trans ‐selective manner was achieved by addition of the Seebach–Fráter enolate to trans ‐hex‐4‐en‐1‐al rather than to trans ‐hex‐3‐en‐1‐al. The type‐ c furanone cores of the synthetic materials were reached by single or double acylation of a model γ‐hydroxy‐β‐oxo ester (compound 50 ) and its hexadiene‐containing counterpart 29 . Our syntheses confirmed the novel connectivities in six compounds. In addition, they required revision of the configuration of a quaternary carbon atom in five cases. Moreover, they allowed elucidation of the configurations of four previously unassigned stereocenters. Hindsight analyses of why the furanone cores of the title compounds had been misinterpreted as a and/or b instead of c are given. Why the stereocenters in the heterocycles had been incorrectly configured, on the bases (a) of relay studies in the 1960s, and (b) of a 1984 total synthesis of gregatin B, is also discussed.