di-π-methane rearrangement

photochemical reaction of a molecular entity comprising two π-systems, separated by a saturated carbon atom (a 1,4-diene or an allyl-substituted aromatic analogue), to form an ene- (or aryl-) substituted cyclopropane.
The @R05194@ formally amounts to a 1,2 shift of one ene group (in the diene) or the aryl group (in the allyl-aromatic analogue) and 'bond formation' between the lateral carbons of the non-migrating @M03968@.
See also: aza-di-π-methane rearrangement, di-π-silane rearrangement, oxa-di-π-methane rearrangement
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 325 (https://doi.org/10.1351/pac200779030293)