Olefins, activated vinylphosphonates

The Baylis-Hillman reaction has become a very powerful carbon-carbon bond forming reaction in the past 20 years. A typical reaction involves an activated olefin (i.e., an acrylate) and an aldehyde in the presence of a tertiary amine such as diazobicyclo-[2.2.2]octane (DABCO) to form an a-meihylhydroxyacrylale. A host of activated olefins have been utilized including acrylates, acroleins, a, 3-unsaturated ketones, vinylsulfones, vinylphosphonates, vinyl nitriles, etc. The Baylis-Hillman has been successfully applied inter- and intramolecularly. In addition, there are numerous examples of asymmetric Baylis-Hilhnan reactions. Reviews (a) Ciganek, E. Org. React. 1997, 51, 201-478. (b) Basavaiah, D. Rao, P. D. Hyma, R. S. Tetrahedron 1996, 52, 8001-8062. (c) Fort, Y. Berthe, M. C. Caubere, P. Tetrahedron 1992, 48, 6371-6384. 

Reductive Addition. Radical addition to activated olefins with alkyl bromides to form a carbon-carbon bond can be also carried out in the presence of TPDS initiated by AIBN in ethanol. Other activated olefins such as diethyl vinylphosphonate and ethyl acrylate can be also used in the addition reaction. The reductive addition of 1-bromoadamantane to diethyl vinylphosphonate with TPDS initiated by AIBN to form the corresponding diethyl 2(l-adamantyl)ethylphosphonate in good yield is shown in eq 4. 

The addition reaction with other alkyl bromides and xanthates to activated olefins such as phenyl vinyl sulfone and diethyl vinylphosphonate, with TPDS-AIBN, also gives the corresponding reductive addition products in moderate to good yields (40-84%). Unfortunately, reductive addition of chalcogenides to activated olefin with the TPDS-AIBN method does not work effectively due to the lower reactivity of chalcogenides toward the... 

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