ChemInform Abstract: [2 + 2] Photocycloaddition of Cinnamates in Flow and Development of a Thiourea Catalyst.

Abstract

2 + 2] Photocycloaddition of Cinnamates in Flow and Development of a Thiourea Catalyst. -The bis(thiourea)-catalyzed dimerization of cinnamates (I) in a flow photoreactor gives rise to diaryl-cyclobutanedicarboxylates as a mixture of diastereomers (II) and (III). -(TELMESANI, R.; PARK, S. H.; LYNCH-COLAMETA, T.; BEELER*, A. B.; Angew.

The Hitchhiker’s Guide to Flow Chemistry

“…64 In an attempt to extend the scope of this transformation to more challenging starting materials, Beeler and co-workers studied the [2 + 2] photocycloaddition of methyl cinnamate 328 in flow (Scheme 135). 663 Initial experiments using a coil reactor illuminated at wavelengths above 305 nm gave modest conversions within 8 h. On the basis of earlier reports using macromolecular host−guest systems, 664,665 the authors hypothesized that this process can be improved by a dual hydrogen-bonding catalyst to template the substrates and thus facilitate dimerization. Moreover, the catalyst could further contribute to reaction enhancement by lowering the HOMO/ LUMO gap of the coupling partners.…”

Recent Advances in the Synthesis of Cyclobutanes by Olefin [2 + 2] Photocycloaddition Reactions

“…The ability of bis(thioureas) to template the [2 + 2] photodimerization of cinnamates was probed by the Beeler group in a flow chemistry setup. 261 They found an improved diastereoselectivity in favor of the δ-truxinate (e.g., 125 → rac-127) versus the β-truxinate upon catalytic (8 mol%) addition of template 126 (Scheme 40). NMR studies suggested binding of the cinnamate to the bis(thiourea) and supported the suggested templating effect.…”