Intramolecular photo-cyclization and consecutive rearrangement reactions of diazo-functionalized olefin-esters

A study on intramolecular photo-cyclization reactions with diazo-functionalized olefin-esters is presented. On irradiation of diphenyl diazo methane esters of cinnamic acids, not only the expected addition to the CC double bond is observed, yielding cyclopropanes, but also the addition to the carboxylic CO double bond is postulated as an intermediate. These formed intermediates undergo a rearrangement to cyclobutanones which further rearrange photo-assisted to oxetanes.Both were isolated and characterized. The reaction progress, the impact of the irradiation wavelength and solvent as well as the influence of the electron density of the olefin on the product distribution is described. Also, the detailed reaction mechanism for the photo-reaction cascade is discussed.

Figure optionsDownload as PowerPoint slideHighlights
► A new reaction pathway was discovered for carbenes, generated from diazo compounds by irradiation.
► Not only the well-known addition of the carbene to a double bond is observed.
► Also (and indeed as main pathway) the formation of an oxetane compound is found.