Site selectivity trisubstituted alkenes

TABLE 1. Site selectivity of the photooxygenation of trisubstituted alkenes (cis effect) ... 

In trisubstituted alkenes with highly crowded cis alkyl groups, the site selectivity (Section II.A.l) does not apply. In those cases the one and only allylic hydrogen, which... 

Table 1 Site Selectivity of the Photo-Oxygenation of Trisubstituted Alkenes (cis Effect)3...

In trisubstituted alkenes with the cis alkyl groups highly crowded, the site selectivity (Sec. II.C) does not apply. In those cases, usually only one allylic hydrogen is available in the more crowded side, not sufficient to stabilize the proper transition state that could produce syn products. Instead, the major product is now produced by abstraction of the allylic hydrogen in the less substituted side of the double-bond anti selectivity [69], These results are summarized in Scheme 9. Photo-oxygenation of trisubstituted acyclic 15-17 [69] and cyclic 18 [70] and 19 [9] alkenes illustrates impressively a strong preference for hydrogen abstraction on the less substituted side of the double bond. 

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