Journal of Organic Chemistry 2012-02-03

Phospha-Michael additions to activated internal alkenes: steric and electronic effects.

Heather K Lenker, Marcia E Richard, Kyle P Reese, Anthony F Carter, Jason D Zawisky, Eric F Winter, Timothy W Bergeron, Krysta S Guydon, Robert A Stockland

文献索引：J. Org. Chem. 77(3) , 1378-85, (2012)

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摘要

The addition of P(O)-H bonds to internal alkenes has been accomplished under solvent-free conditions without the addition of a catalyst or radical initiator. Using a prototypical secondary phosphine oxide, a range of substrates including cinnamates, crotonates, coumarins, sulfones, and chalcones were successfully functionalized. Highly activated acceptors such as isopropylidenemalononitrile and ethyl 2-cyano-3-methyl-2-butenoate underwent the phospha-Michael reaction upon simple trituration of the reagents at room temperature, whereas less activated substrates such as ethyl cinnamate and methyl crotonate required heating (>150 °C) in a microwave reactor to achieve significant consumption of the starting alkenes. For the latter alkenes, a competing reaction involving disproportionation of the ditolylphosphine oxide into ditolylphosphinic acid and ditolylphosphine was observed at the high temperatures needed to promote the addition reaction.