143618-84-2Relevant articles and documents
Photochemical Reactions of Alkenyl Phenylglyoxylates
Hu, Shengkui,Neckers, Douglas C.
, p. 6820 - 6826 (2007/10/03)
The photochemical reactions of alkyl phenylglyoxylate esters whose ester function contains double bonds of differing substitution, situated at varying distances from the carbonyl group, have been studied. The intramolecular Paterno-Buechi reaction is the dominating photoreaction when an electron rich alkenyl group is situated at the proper distance as in 1′,5′-dimethylhex-4′-enyl phenylglyoxylate (6). When the distance between the excited carbonyl group and the same alkenyl function is increased, as it is in 3′,7′-dimethyl-6′-octenyl phenylglyoxylate (7), intramolecular γ-hydrogen abstraction (Norrish type II) products, as well as the products of intramolecular photocycloaddition, are observed. We suggest this to be the result of a competitive distant dependent electron transfer reaction between the excited carbonyl group and the alkene. A longer distance of separation between these two reactive functions decreases the efficiency of formation of the cycloaddition product. When the separation of the same alkene from the glyoxylate is shortened as in 4′-methylpent-3′-enyl phenylglyoxylate (5), electron transfer-induced remote proton abstraction leading to cyclol formation occurs, in addition to the Paterno-Buechi reaction. Further reducing the distance as in 3′-methylbut-2′-enyl phenylglyoxylate (3) results in only the normal intramolecular (Norrish type II) and intermolecular hydrogen abstraction products. At a distance where both oxetane and cyclol formation are possible as in 5, decreasing the electron richness of the alkenyl group as in cis-3′-hexenyl phenylglyoxylate (cis-4) eliminates the oxetane product. Formation of cyclol is shown to be conformationally controlled in that a similar product is not observed to be formed from trans-3′-hexenyl phenylglyoxylate (trans-4). If both the electron richness of the alkenyl group and the distance of separation are decreased as in 2′-hexenyl phenylglyoxylate (2), only γ-hydrogen abstraction products result. Cis-trans isomerization of the olefln is not observed in either 2 or 4.
