Asymmetric total syntheses of teretifolione B and methylteretifolione B via Diels-Alder reaction of optically active pyranobenzyne and substituted furans

We report the asymmetric total syntheses of teretifolione B and methylteretifolione B, which are benzochromenes originally isolated from Conospermum plants. The synthesis involves enzymatic asymmetric transesterification of racemic acetoxychromene and construction of the basic framework via Diels-Alder reaction of optically active pyranobenzyne and substituted furans. The absolute configuration of the chiral chromene was unambiguously determined by asymmetric total synthesis of teretifolione B and its characterization. The first asymmetric total synthesis of methylteretifolione B was achieved in a similar manner and its absolute configuration, for which direct proof has not been reported, was established. (C) 2017 Elsevier Ltd. All rights reserved.