Explorations In Novel Photochemical Modes Of Radical-Alkene Reactivity: My Piece Of The Pi

The formation of Csp3-Csp3 bonds is arguably the most critical yet challenging transformation in organicsynthesis. For many years the Michael addition, which utilizes highly reactivity organometallic carbon nucleophiles which are “poised to react”, was used to achieve hydroalkylation of activated alkenes. Furthermore, this mode of reactivity also offered the potential to use other electrophiles to perform vicinal (1,2) alkene difunctionalization. Though effective in many contexts, this reaction is often plagued by functional group incompatibilities, poor 1,2 vs 1,4 addition selectivity and unstable precursors. In contrast to organometallic carbanions, carbon-centered radicals display markedly higher regioselectivly in additions to alkenes and demonstrate much improved chemoselectivity. The Giese addition utilizes carbon radicals, typically generated from alkyl halides via halogen atom abstraction, to engage in radical addition with activated alkenes. Unfortunately, the harsh conditions and reagents required for the radical chain mechanisms employed in Giese reactions restrict the transformation to alkene hydroalkylations with minimal functional group compatibility. However, several modes of photochemical catalysis can be used for radical generation which are significantly milder and more tolerant than typical radical initiation used in classical Giese addition protocols. These catalytic mechanisms offer the potential for further functionalization of radical addition intermediates opening the door a wide variety of alkene difunctionalizations with dramatically improve functional group compatibility compared to classical vicinal difunctionalizations. Herein are reported personal explorations in novel radical alkene reactions facilitated via photochemical modes of catalysis.