1984 Volume 57 Issue 6 Pages 1604-1607
Irradiation of 2,2-dimethyl-1-phenyl-1,3-diketones with 3-ethyl or 3-isopropyl substituents gave type II cyclization product, 3-hydroxy-2,2,4-trimethyl-3-phenylcyclobutanone or 3-hydroxy-2,2,4,4-tetramethyl-3-phenylcyclobutanone, along with type I cleavage products. The type II cyclization/type I cleavage ratio is greater with a 3-isopropyl group than with a 3-ethyl group. A similar irradiation of 2,2-dimethyl-1-phenyl-1,3-butanedione gave type I cleavage products and no type II cyclization product. Irradiation of 2,4-dimethyl-1-phenyl-1,3-pentanedione gave 3-hydroxy-2,2,4-trimethy1-3-phenylcyclobutanone and propiophenone. The geometry of 3-hydroxy-2,2,4-trimethyl-3-phenylcyclobutanone which arose from 2,2-dimethyl-1-phenyl-1,3-pentanedione was cis with respect to phenyl and 4-methyl groups and that which arose from 2,4-dimethyl-1-phenyl-1,3-pentanedione was trans.
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