Transannular reactions of cycloalkenes, cycloalkadienes and cycloalkatrienes. 16. Photocyclization of cyclononene and cycloundecene
摘要:
Irradiation of cyclononene (7b) and cycloundecene (7d) in pentane afforded cis-bicyclo[4.3.0]nonane (10b) and cis-bicyclo[6.3.0]undecane (10d), respectively. Small amounts of the fragmentation products 1-undecene (14d) and 1-undecyne (15d) were also obtained from cycloundecene (7d). The photobehavior of the series of medium- and large-ring alkenes 7a-e is compared. Aside from E reversible Z isomerization, the principal pathway in each case involves rearrangement of the pi,R(3s) excited state to the cycloalkylidene intermediate 8, which undergoes predominant, if not exclusive, 1,5-transannular insertion to afford the corresponding cis-bicyclo[n.3.0]alkane (10). The cycloalkylidenes 8 formed in this way exhibit behavior somewhat different from those generated by other methods. The possible contributory role of carbene intermediates derived from pi,R(3s) excited states in E revesible Z photoisomerization of acyclic alkenes is also discussed.
The first metal-catalyzed intramolecular [5+2] cycloadditions of vinylcyclopropanes and alkenes: Scope, stereochemistry, and asymmetric catalysis
作者:Paul A. Wender、Craig O. Husfeld、Elke Langkopf、Jennifer A. Love、Norbert Pleuss
DOI:10.1016/s0040-4020(98)00355-x
日期:1998.6
The firststudies of the metal-catalyzed [5+2] cycloadditions of vinylcyclopropanes and alkenes are described. These reactions proceed with exceptional diastereoselectivity and in good to excellent yields. The effect of tether and substituent variations are examined. In addition, preliminary studies show that enantioselective cycloadditions can be achieved through the use of catalysts modified with