Whereas cyclopentenylcarbenes resulting from photocycloaddition of 4-alk-1-ynylcoumarins to 2,3-dimethylbut-2-ene undergo tandem cyclization to hitherto unknown tetracyclic (4-hetera)cyclopent[b, c]acenaphthylenes, the corresponding cyclopentenylnitrenes stemming from 4-cyanocoumarins and the same alkene are converted into tricyclic imines via H-abstraction.
Photochemical Synthesis of Cyclopenta[<b><i>c</i></b>]-Anellated Benzopyrans and Benzothiopyrans
作者:Paul Margaretha、Dirk Schwebel、Marko Soltau
DOI:10.1055/s-2001-15053
日期:——
On irradiation in the presence of 2,3-dimethylbut-2-ene the newly synthesized 2-oxo-2H-1-benzopyran- and 2-oxo-2H-1-benzothiopyran-4-carbonitriles are converted selectively to a cyclopenta[c]benzopyran or -thiobenzopyran, respectively. The reaction proceeds via addition of the alkene to the nitrile- and olefinic C-atoms of the triplet excited coumarin derivatives.