UNEXPECTED REGIOSELECTIVE DIELS-ALDER CYCLOADDITION REACTIONS BETWEEN 3-FLUOROBENZYNE AND 2-ALKYLFURANS

Article abstract of DOI:10.1016/S0040-4039(00)82311-4

The Diels-Alder reaction between 3-fluorobenzyne (1) and 2-alkylfurans (2) gives a mixture of syn adduct 3 and anti adduct 4.The syn cycloadduct invariably predominates and the regioselectivity increases in the order: R= Me< Et< i-Pr< t-Bu, to a maximum of 90percent syn adduct 3d for 2-tert-butylfuran.These results are rationalized in terms of a concerted nonsynchronous transition state that reflects an alkyl steric effect and a polarized aryne 1.