Benzocyclobutene, ring expansion

Dioxane from 2-a-hydroxy-2-spiro-l,3-dioxolane ring with benzocyclobutene ring expansion... 

It was also found that the ring expansion could be accomplished photo-chemically, from either phenyldiazomethane or triplet phenylcarbene.7 Both the thermal and photochemical ring expansions were found to be reversible,5c, thus providing rare examples of carbene-to-carbene interconversions. One remarkable example of this reversibility is the interconversion of the isomeric tolylcarbenes upon pyrolysis — the ultimate products of which include styrene and benzocyclobutene (Scheme 3).6,8,9... 

The dipolar cycloaddition of sydnones (l,2,3-oxadiazolidin-5-one derivatives) (108) with benzocyclobutene (109) has been used to synthesize 3 f-2,3-benzodiazepines (110). This synthesis involves a cycloaddition-extrusion-ring-expansion sequence, and with other mesionic compounds, for example the thiazolium-4-olate (111), primary cydoadducts (112) were isolated (Scheme 13)... 

Suzuki T, Hamura T, Suzuki K. Ring selectivity successive ring expansion of two benzocyclobutenes for divergent access to angular and linear benzanthraquinones. Angew. Chem. Int. Ed 2008 47 2248-2252. 

Switlak, K., He, D., and Yates, P, Intramolecular trapping of an oxacarbene intermediate in the photochemical ring expansion of a cyclopentanone,/. Chem. Soc., Perkin Trans. 1, 2579, 1992. Staab, H. A. and Ipaktschi, J., Photochemische reaktionen des benzocyclobuten-1, 2-dions, Chem. 

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