Photochemical [2+2]-cycloaddition of cyclic α,β-enones to monosubstitüted acetylenes
1979; Elsevier BV; Volume: 35; Issue: 1 Linguagem: Inglês
10.1016/0040-4020(79)85011-5
ISSN1464-5416
AutoresE. P. SEREBRYAKOV, S. D. KULOMZINA‐PLETNEVA, A. Kh. Margaryan,
Tópico(s)Oxidative Organic Chemistry Reactions
ResumoThe photo addition of cyclic α,β-enones to monosubstituted acetylenes gives substituted bicyclo [3,2,0]hept-6-en-2-ones and bicyclo[4,2,0]oct-7-en-2-ones. The addition of 2-cyclopentenone to different substrates of type RCCH (where R is alkyl, CH2X, OEt, COOMe and also Ph) and addition of 2-cyclohexenones to 1-hexyne show a linear correlation between the σ-constants of substituents and the rates of cycloaddition. The reaction can be qualified as a moderately electrophilic attack of the enone triplet on the acetylenic bond (¦ϱ¦~1.5). Temperature and solvent effects on the rates and regioselectivity were also studied. The regioselectivity of addition of these α, β,-unsaturated ketones to 1-alkynes does not correspond to what might be expected on the basis of Corey's orientation rule. The addition of 2-cyclopentenone to ethoxyacetylene 3g and to methyl propiolate3h proceeds with surprisingly low regioselectivity while phenylacetylene 3i undergoes only dimerization under photoannelation conditions.
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