Hexynes photocycloaddition

The intermolecular ortho photocycloaddition of acetylenes to benzene has provided routes to cyclooctatetraenes [78-84], Intramolecular photocycloaddition of alkynes to aromatic rings is also investigated. Morrison et al. reported that photolysis of 6-phenyl-2-hexyne in hexane solution using 254-nm light leads to the formation of bicyclo[6.3.0]undecatetraene (251 and/or 252) [284] (Scheme 70). Pirrung prepared various bicyclo[6.3.0]undecatetraenes (254a-e) by the in-... 

Investigation of [2 -l- 2] photocycloaddition of enones to monosubstituted alkynes indicates that the reaction proceeds with an opposite regioselectivity compared to that of alkenes [71]. Generally, head-to-head adducts are major products except when the group substituted on the alkyne is -CO2R or -OR (see Scheme 17). Thus, methyl propynoate (60, R = CO2CH3) photoadds to cyclopentenone 59 to give 1 1 HH and HT products. Cycloaddition of cyclohexenone to 1-hexyne has also been studied and the HH HT ratio varies from 2 1 to 7 1 as a function of substituents at the enone 3-position. It... 

Cavazza, M. and Zandomeneghi, M., Photocycloaddition of acetylene and 1-hexyne to 4-acetox-ycyclopent-2-en-l-ones. Intermolecular asymmetric photosyntheses induced by circularly polarized light, Gazz. Chim. Ital, 117,17,1987. 

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