Photocyclization enantiodifferentiating

There has been considerable interest in various photocycloaddition reactions over the last years which not only broadened the number of useful photochemical applications but also revealed further mechanistic insight into these reactions [76,77]. Among these reactions, reports focusing on either the [2 -h 2] or the [4 -I- 2] cycloaddition, are numerous. Also the efforts toward the enantiodifferentiating photosensitization in photocyclization reactions have to be mentioned [78],... 

Ramamurthy, Scheffer and coworkers and other investigators reported the enantiodifferentiating Norrish/Yang photocyclization [49-53] of aryl cis-4-tert-buty -cyclohexyl ketones 1 to cyclobutanols 2 (Scheme 1) in chirally modified zeolite supercages [49]. 

Enantiodifferentiating photocyclizations of prochiral 18a-e in zeolites modified with ephedrine, norephedrine, pseudoephedrine, menthol, and 1-pheny lethylamine gave 19a-e in moderate ees of up to 44% (obtained for 18a ill (— )-norephedrine-immobilized NaY). Diastereodifferentiating photocyclizations... 

The most successful supramolecular photochirogenesis with chirally modifiea zeolites is the enantiodifferentiating photocyclization of tropolone derivatives in[ zeolites modified with (— )-ephedrine or (— )-norephedrine, giving bicyclo[3.2.0J heptadienes in high ees. It is interesting to compare this result with the highlj ... 

Enantiodifferentiating photocyclizations of tropolone methyl and phenethyl ethers 22a and 22b were also examined in isotropic and anisotropic media (Scheme 8). Although the photolyses of 22a and 22b gave racemic 23a and 23b... 

---