[2+2] Cycloadditions
Intramolecular [2+2] Photoaddition/Cyclobutane-Fragmentation Sequence in Organic Synthesis,
Oppolzer, W. Acc. Chem. Res. 1982, 15, 135.
Synthetic Applications of Intramolecular Enone-Olefin Photocycloadditions,
Crimmins, M. T. Chem. Rev. 1988, 88, 1453.
Cycloadditions of Fluoroallene and 1,1-Difluoroallene,
Dolbier, W. R., Jr. Acc. Chem. Res. 1991, 24, 63.
Asymmetric Synthesis of β-Lactams by Staudinger Ketene-Imine Cycloaddition Reaction,
Palomo, C.; Aizpurua, J. M.; Ganboa, I.; Oiarbide, M. Europ. J. Org. Chem. 1999, 3223-35.
[2+2] Photocycloaddition/Fragmentation strategies for the synthesis of natural and unnatural products,
Winkler, J. D.; Bowen, C. M.; Liotta, F. Chem. Rev. 1995, 95, 2003.
Stereoselective Intermolecular [2+2]-Photocycloaddition Reactions and their Application in Synthesis,
Bach, T. Synthesis 1998, 683.
Concerted thermal [2 + 2] cycloadditions are symmetry forbidden in the usual suprafacial process (4e Huckel process). However, photochemical cycloadditions are allowed reactions, and many examples of their use in synthesis have been reported.
Ketenes react with alkenes to give cyclobutanones, a reaction thought to occur by an allowed π2s + π2a cycloaddition - suprafacially on the alkene, but by an unusual antarafacial addition across the ketene double bond (4e Moebius transition state).
Sativene: Sigrist, R.; Rey, M.; Dreiding, A. Helv. Chem. Acta 1988, 71, 788.
Clovene: Funk, R. L.; Novak, PM.; Abelman, M. M Tetrahedron Lett. 1988, 29, 1493.
Ginkgolide B: Corey, E. J.; Kang, M. C.; Desai, M. C.; Ghosh, A. K.; Houpis, I. N. J. Am. Chem. Soc. 1988, 110, 649-651. DOI
