Methyl (α-naphthyl) acrylates bearing an ortho-substituent with a hydrogen atom produce naphthocyclobutenes upon Ir(Fppy) 3 -mediated photosensitization. This reaction can be described as a carbon analogue of the Norrish−Yang reaction: upon triplet excitation of the acrylate a 1,5-HAT results in a 1,4-diradical which forms the cyclobutene. Diastereoselectivities up to >20:1 were observed for the ring-closure reaction.
A general synthetic
entry to functionalized dihydrophenalenes has
been found using naphthyl-cyclopropane esters as starting materials.
The desired annulation was possible with visible light, Ir(Fppy)3 as photocatalyst, BnNMe2 or DABCO as electron
donor, HAT-catalyst, and proton source. A broad scope of substituted
naphthyl and azanaphthyl derivatives provided the photoannulation
products in high yield. Deuteration studies support a photoredox mechanism
involving the photoreductive cyclopropane opening to an enolate radical
followed by an aryl radical trapping.
Converting biomass into value‐added chemicals is of significant interest and we report an efficient hydrosilylation to convert levulinic acid to γ‐valerolactone using cost‐effective silanes such as PMHS and TMDS with B(C6F5)3 as catalyst. This metal free methodology works at room temperature reaching TONs and TOFs up to 16000 and 2000 h−1. Insights into the reaction mechanism are reported.
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