Allene-tethered enones

The photocycloaddition of allene-tethered enones, like 344, affords the expected adducts 345 in 67-90 % yields. The reaction proceeds with an enantioselectivity of > 99... 

The mechanistic rationale of the Cl sequence provides reactive intermediates such as enones and elusive allenols (vide supra) that can be exploited even in a domino sense, if a suitable trapping functionality is present. For the synthesis of heterocycles two bimolecular sequences have been elaborated. One is terminated by an intramolecular cyclocondensation with an amino group, which is unprotected and carried through the sequence to trap the evolving enone functionality. The other exploits the generation of a vinyl allene intermediate, which is captured by an intramolecularly tether dienophile in the sense of a (4+2)-cycloaddition. 

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