Vinyl acetate, photocycloaddition reactions

The scope of this approach was widened by the observation of excellent enantioselectivities in intermolecular [2+ 2]-photocycloaddition reactions with various alkenes [62,71]. In the presence of an excess amount of alkene, 4-me thoxy-2-quinolone (57) was converted with high chemo- and regioselectivity to the exo and endo cyclobutanes 59 and 60. With 4-penten-1-ol (58a), allyl acetate (58b), methyl acrylate (58c), and vinyl acetate (58d), the exo diastereomers 59a-d were formed with high simple diastereoselectivity and in high yields (80-89%), Under optimized irradiation conditions (2.4 eq. of host 44 or ent-44, — 60°C), high enantiomeric excesses were achieved in all instances, as depicted in Scheme 22. These enantiomeric excesses are unprecedented for an intermolecular photochemical reaction. 

Benzo[b]thiophene 1,1-dioxide 38 undergoes [2+2] photocycloaddition with vinyl acetate [120] and l-(diethylamino)propyne [121] to give the corresponding adducts in excellent yields (Scheme 22). The reaction appears synthetically important, and its scope and limitation deserve examination in detail. 

The regiochemical and stereochemical courses of the photocycloaddition of A-acylindoles with monosubstituted olefins such as methyl acrylate and vinyl acetate, as well as the possible mechanistic pathways for these reactions, have been the subject of several reports. In one of the earliest examples, the photocycloaddition of 1 -benzoylindole (8) and methyl acrylate (9) produced the compound 10, which was then converted via a short synthetic sequence to a variety of 2a,7b-dihydrocyclobut[h]indole derivatives 11 (Scheme 2). These compounds were in turn converted to the corresponding l//-l-benzazepines 12, through silver ion-catalyzed thermolysis reactions at 100-160°C [14, 15]. 

The Paterno-Buchi reaction, as well as the photocycloaddition of cyclo-hexenones with vinyl acetates or vinyl ethers, have been carried out with energy-saving compact light sources, using continuous microflow photoreactors. 

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