Modular catalysts for diene cycloisomerization: rapid and enantioselective variants for bicyclopropane synthesis

Abstract

Deconstructing the tridentate (triphos)Pt(II) first-generation catalysts into mixed diphosphine/monophosphine combinations (P(2)P) has led to new, more active catalysts for the cycloisomerization of 1,6-, and 1,7-dienes into bicyclo-[3.1.0] and -[4.1.0] products. When the diphosphine was the small bite angle dppm, reaction rates were approximately 20-fold faster than with triphos, although reaction rates and diastereoselectivities were also sensitive to the monophosphine (PMe(3) being optimal for rate, PPh(3) being optimal for selectivity). When the diphosphine was xyl-BINAP or SEGPHOS, the catalysts were enantioselective, and enantio-ratios up to 98:2 were observed. Both sets of catalysts showed enhanced functional group tolerance in comparison to the original (triphos)Pt(2+) catalyst. X-ray structures for both precatalysts are also reported.