Photochemical transformations. XI. Photochemical and thermal rearrangements of some .beta.-substituted allylic systems

Abstract

The photochemistry of /3-chloro-and /3-phenylcinnamyl and -crotyl chlorides has been investigated. These compounds, under both sensitized and direct irradiation, undergo cis-trans isomerizations and allylic rearrangements. The photostationary states contain substantial amounts of the thermally less stable secondary isomers. Sensitized irradiation of d-chlorocinnamyl p-toluenesulfonate and methanesulfonate also resulted in cis-trans isomerizations and rearrangements. Quantum yield and quenching results are reported and possible reaction mechanisms are discussed.

Photochemical transformations. 20. Intermediates in the sensitized photorearrangements of the .alpha.- and .gamma.-methylallyl chlorides

“…That they do not may be seen in Figure 1, where it would seem that there are several intermediates involved in the photosensitized rearrangement of ira«5-crotyl chloride (1-t) to 1-c, 2, and 3-c and 3-t, with the latter two giving rise to the same line and thus presumably arising from the same intermediate. A very simple mechanistic scheme for a triplet-sensitized reaction is given (Scheme I) in eq [5][6][7][8][9][10][11] involving sensitizer S, reactant R, and quencher Q to give a particular product P, where the superscript refers to excited-state multiplicity and 3R-S indicates an excited-state complex.…”