Transposed Paternò–Büchi Reaction

Abstract

A complementary strategy of utilizing ππ* excited state of alkene instead of nπ* excited state of the carbonyl chromophore in a "transposed Paternò-Büchi" reaction is evaluated with atropisomeric enamides as the model system. Based on photophysical investigations, the nature of excited states and the reactive pathway was deciphered leading to atropselective reaction. This new concept of switching of excited-state configuration should pave the way to control the stereochemical course of photoreaction due to the orbital approaches required for photochemical reactivity.

Realizing an Aza Paternò–Büchi Reaction

“…While there are scattered reports on photocycloaddition of imines that feature an electron‐withdrawing group on the nitrogen or cyclic imines, synthetically useful reports are very limited . We recently investigated [2+2]‐photocycloaddition of atropisomeric enamides and showcased that the ππ* excited state of an enamide can add to a carbonyl compound known as the transposed Paternò–Büchi reaction . Driven by curiosity, we decided to explore if [2+2]‐photocycloaddition of enamides with tethered imines was feasible, leading to an aza Paternò–Büchi reaction .…”

“…Driven by curiosity, we decided to explore if [2+2]‐photocycloaddition of enamides with tethered imines was feasible, leading to an aza Paternò–Büchi reaction . As a starting point, we first designed stabilized imines such as hydrazones and oximes as they are suitable for routine synthetic manipulation without hydrolysis (Table ) . The imines were typically obtained as an inseparable mixture of E:Z isomers.…”

Energy Transfer Catalysis by Visible Light: Atrop‐ and Regio‐Selective Intermolecular [2+2]‐Photocycloaddition of Maleimide with Alkenes

“…The knowledge gained in reaction control by confinement, led to the development of various catalytic approaches for asymmetric [2+2]‐photocycloadditions . In this regard, our group has utilized the strategy of employing restricted bond rotations in atropisomeric chromophores to control reactivity and selectivity in solution at ambient conditions . Recently, we uncovered new excited state reactivity of methyl‐substituted maleimide that underwent photoene reaction instead of the traditional [2+2]‐photocycloaddition by differently substituting the alkene .…”

Dual C(sp3)−H Bond Functionalization of N‐Heterocycles through Sequential Visible‐Light Photocatalyzed Dehydrogenation/[2+2] Cycloaddition Reactions

“…Catalytic dehydrogenation [4] has provided anew method for activating two C(sp 3 )ÀHb onds,s ince the reactive alkene intermediate generated by this process could be utilized in as econdary reaction to forge new carbon frameworks. [7] Recently, Zhou and co-workers developed an unprecedented catalytic enantioselective Heck annulation of propargylic acetates and cycloalkenes to obtain highly strained, fused cyclobutenes. [7] Recently, Zhou and co-workers developed an unprecedented catalytic enantioselective Heck annulation of propargylic acetates and cycloalkenes to obtain highly strained, fused cyclobutenes.…”

“…[5] [2+ +2] cycloaddition is one of the most powerful and widely applied transformations in organic chemistry [6] and plays aremarkable role in building strained and unusual molecular architectures that cannot be accessed through other pathways. [7] Recently, Zhou and co-workers developed an unprecedented catalytic enantioselective Heck annulation of propargylic acetates and cycloalkenes to obtain highly strained, fused cyclobutenes. [8] On the basis of all these factors,w ed ecided to tackle the aforementioned difficulty by merging catalytic dehydrogenation with [2+ +2] cycloaddition in as equential process (Scheme 1a).…”