Photosensitized Oxygenation of Twisted 1,3-Dienes: Abnormally Higher Reactivity of Vinyl Hydrogen Rather than Allyl Hydrogen toward Singlet Oxygen
作者:Hajime Mori、Keiichi Ikoma、Sachihiko Isoe、Kazuo Kitaura、Shigeo Katsumura
DOI:10.1021/jo980955o
日期:1998.11.1
As one of the novel examples to investigate the characteristic reactivity of significantly twisted 1,3-dienes, the photosensitized oxygenation of two types of significantly twisted 1,3-dienes, cis-beta-ionol derivative 2 and acyclic derivative Il, is investigated. Photosensitized oxygenation of 2a-f and 11a-e revealed that the vinyl hydrogen Ha was more reactive than the allyl hydrogen Hb. Thus, phenyl derivative 2e and tert-butyl-substituted compound lid selectively produced allenes 3e and 13d in 67% and 75% yield resulting from the ene reaction of the vinyl hydrogen Ha rather than allyl alcohols 4e and 14d resulting from the allyl hydrogen abstraction in 24% and 8% yield, respectively. Furthermore, in the case of methyl-substituted compound 11b, the extent of the inherent reactivity of the vinyl hydrogen Ha was similar to that of the allyl hydrogen He. On the basis of X-ray analysis and NIM and MO calculations, the discovered abnormally higher reactivity of the vinyl hydrogen would be rationalized by considering mainly the large sigma*-pi orbital interaction between the vinyl C-H bond and another double bond in significantly twisted 1,3-dienes resulting from calculations of HOMO electron densities.