jo202183u_si_001.pdf (3.62 MB)
Phospha-Michael Additions to Activated Internal Alkenes: Steric and Electronic Effects
journal contribution
posted on 2012-02-03, 00:00 authored by 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. StocklandThe 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.