Photodriven Dehydrogenative Homocoupling of Benzylic C–H Bonds Forming Strained C–C Bonds

Abstract

A photoinduced dehydrogenative homo-coupling reaction of alkylarenes is reported. Gaseous hydrogen is evolved as the sole byproduct and neither oxidants nor hydrogen acceptors are required. The present reaction offers an environmentally benign and atom-economical means for forming sterically strained C–C single bonds. It also gives a remarkable example of photo-driven reactions overcoming a considerable rise in energy.

Reduction of 2-H-substituted pyrrolinium cations: the carbon–carbon single bond in air stable 2,2′-bipyrrolidines as a two-electron-source

“…In this respect, we focused in particular on investigating their probable follow-up chemistry, such as dimerisation, hydrogen abstraction, and hydrogen elimination as previously reported for other species. 6 Dimerisation should lead to the formation of 2,2′-bipyrrolidine derivatives V , which was indeed observed with N -alkyl substituents. The C2-centre of the pyrrolidine-motif in V is sterically hindered and bears heteroleptic substituents with sp 3 - N -centres at adjacent positions.…”

Synthetic Applications of Photocatalyzed Halogen‐Radical Mediated Hydrogen Atom Transfer for C−H Bond Functionalization

“…A similar approach was also used for the dehydrogenative homocoupling of benzylic CÀ H bonds. [94] The same group reported also two dehydrogenative strategies based on the generation of bromine radicals for the synthesis of esters by coupling primary alcohols or aldehydes with phenols. [95,96] Recently, a similar approach for the dehydrogenative coupling of aldehydes and alkyl arenes in flow was reported.…”

“…If on one side the cross‐coupling did not work with electron‐poor alkyl arenes, on the other side α‐branched aldehydes gave the corresponding products in good results despite the more marked steric hindrance (see compounds 18.9–18.10 ). A similar approach was also used for the dehydrogenative homocoupling of benzylic C−H bonds [94] …”

Photocatalytic Desulfonylative Homocoupling of Benzylic Sulfone Derivatives

“…6 Specifically, Ishida and Murakami have developed an ideal dehydrogenative homocoupling of alkylarenes using Ni/Ir dual catalysis. 7…”