title: Phospha-Michael additions to activated internal alkenes: steric and electronic effects.
abstract: 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.
authors.affiliation: Department of Chemistry, Bucknell University, Lewisburg, Pennsylvania 17837, USA.
authors.forename: Heather K
authors.initials: HK
authors.lastname: Lenker
authors.forename: Marcia E
authors.initials: ME
authors.lastname: Richard
authors.forename: Kyle P
authors.initials: KP
authors.lastname: Reese
authors.forename: Anthony F
authors.initials: AF
authors.lastname: Carter
authors.forename: Jason D
authors.initials: JD
authors.lastname: Zawisky
authors.forename: Eric F
authors.initials: EF
authors.lastname: Winter
authors.forename: Timothy W
authors.initials: TW
authors.lastname: Bergeron
authors.forename: Krysta S
authors.initials: KS
authors.lastname: Guydon
authors.forename: Robert A
authors.initials: RA
authors.lastname: Stockland