Sequential directed ortho metalation-boronic acid cross-coupling reactions. A general regiospecific route to oxygenated dibenzo[b,d]pyran-6-ones related to ellagic acid
作者:B. I. Alo、A. Kandil、P. A. Patil、M. J. Sharp、M. A. Siddiqui、Victor Snieckus、P. D. Josephy
DOI:10.1021/jo00012a004
日期:1991.6
A general regiospecific synthesis of dibenzo[b,d]pyran-6-one derivatives 1a,c and 8a-i related to ellagic acid is described (Scheme I, Table I). The sequence involves directed ortho metalation-boronation of benzamides 4 to give the arylboronic acids 5, which, upon palladium-catalyzed cross-coupling with alkoxybromobenzenes 6 leads to the biphenylamides 7. BBr3 demethylation followed by acid-catalyzed cyclization affords pyranone 8. In this manner, the naturally occurring dibenzopyranones 1a, autumnariol (1c), and the heterocyclic analogue 13 (Scheme III) were efficiently prepared.