title: Efficient photocyclization of o-alkylbenzaldehydes in the solid state: direct observation of E-xylylenols en route to benzocyclobutenols.
abstract: The photocyclization to benzocyclobutenols of o-alkyl aromatic aldehydes that are predestined for gamma-hydrogen abstraction is found to occur efficiently in the solid state; in contrast, solution-phase photolysis is known to afford a mixture of several products. It is shown that mesitaldehyde, which is a liquid, also undergoes efficient cyclization when subjected to photolysis as a solid inclusion complex. The marginal energy differences in the relative energies of the E-enols and the corresponding cyclobutenols in the case of cyano-substituted mesitaldehydes has permitted direct observation, for the first time, of the E-enols en route to benzocyclobutenols. The AM1 calculations suggest that the cyano-substitution causes intrinsic stabilization of the E-enols relative to the corresponding cyclobutenols, while the bromo groups do the opposite. The lack of observation of the red color in bromo- and formyl-substituted aldehydes is attributed to rapid cyclization of the E-enols to the their respective cyclobutenols even at low temperatures.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Kanpur 208 016, India. moorthy@iitk.ac.in
authors.forename: J N
authors.initials: JN
authors.lastname: Moorthy
authors.forename: P
authors.initials: P
authors.lastname: Mal
authors.forename: R
authors.initials: R
authors.lastname: Natarajan
authors.forename: P
authors.initials: P
authors.lastname: Venugopalan