Dearomative 1,6-addition of P(O)–H to in situ formed p-QM-like ion pairs from 2-benzofuryl-ols to C3-phosphinoyl hydrobenzofurans

Abstract

A dearomative C3-phosphorylation of 2-benzofuryl-ols with the P(O)–H species to C3-phosphinoyl hydrobenzofurans has been established. The key to achieve the high C3-regioselectivity is the use of an “OMe” group at the C6-position to enable the dearomative 1,6-addition of P(O)–H compounds to para-quinone methide (p-QM)-like ion pairs generated in situ from 2-benzofuran-ols. A “one-pot” tandem C3-phosphorylation/aromatization to C3-phosphinoyl benzofurans is also developed. This protocol not only provides an alternative method for the synthesis of C3-phosphinoyl hydrobenzofurans and benzofurans but also represents a new strategy for the dearomatization of benzofurans.