Topochemical Selectivity in Solid-State Photorearrangement: Conformational Control in Photorearrangements of cis-1,2-Dibenzoylalkenes

Visible light-driven dearomative ring expansion of (aza)arenes to access dihydrofuran-based polycyclic compounds

The dearomative expansion of aromatic rings has long been pursued by chemists due to its potential to provide tractable approaches for synthesizing valuable non-aromatic molecules. To circumvent the conventional use of hazardous and unstable diazo compounds, photochemical synthesis has recently emerged as a promising platform. However, protocols that can effectively handle both arenes and azaarenes remain scarce. Herein, we introduce a generic strategy that efficiently converts β-(aza)aryl-β-substituted enones into biologically significant cycloheptatriene derivatives, including their aza-variants. This method allows for the easy modulation of diverse functional groups on the product and demonstrates a wide substrate scope, evidenced by its excellent tolerance to various drug motifs and good compatibility with five-membered azaarenes undergoing ring expansion. Moreover, DFT calculations of plausible mechanisms have motivated the implementation of an important cascade diradical recombination strategy for 1,3-dienones, thus facilitating the synthesis of valuable 2-oxabicyclo[3.1.0]hex-3-ene derivatives.

Photochemical Access to Substituted β-Lactams and β-Lactones via the Zimmerman-O'Connell-Griffin Rearrangement

A photomediated protocol giving facile access to substituted β-lactam and β-lactones is presented. The method realizes, for the first time, the use of the Zimmerman-O'Connell-Griffin (ZOG) rearrangement in [2 + 2] cycloaddition. Products are obtained in high yield with excellent diastereoselectivity under visible light irradiation and under mild reaction conditions.

Formation of an exceptionally stable ketene during phototransformations of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores

Photochemical reactions of bicyclo[2.2.2]oct-5-en-2-ones having mixed chromophores like a 5,6 dibenzoyl moiety and bulky electron-deficient substituents like phenyl or isopropenyl at the bridgehead position were analyzed for the first time in different solvents and upon irradiation with different wavelengths. In all cases, a regioselective photoinduced 1,5-phenyl migration leading to vinyl ketenes from the more congested site of the molecule to the less congested one has been observed. The ketenes were exceptionally stable both in air and solution. Its stability studies in acetonitrile through time-dependent UV absorption spectra revealed that it remained almost unchanged at least for a couple of weeks.

PET reactions of cis-dibenzoylalkenes: an efficient trans-reduction of C=C bond

In contrast to its reaction under catalytic hydrogenation, the first instance of an exclusive and chemoselective trans-reduction of the ene part of derivatives of 5,6-dibenzoylbicyclo[2.2.2]oct-5-en-2-one has been reported under moderate photoinduced electron transfer (PET) conditions using triethylamine (TEA). In the absence of TEA, such molecules underwent 1,5-photophenyl migration yielding vinyl ketenes.