1 research outputs found
Photocycloaddition of Arenes and Allenes
In
this work, we report on a new intramolecular <i>para</i> cycloaddition of arenes with allenes, yielding attractive rigid
scaffolds bearing several reactive functionalities to build in further
diversity. Bicyclo[2.2.2]octadiene-type products and benzoxepine acetals
are formed in this reaction, in ratios and yields depending on the
substitution pattern on the aromatic ring, the nature of the chromophore,
and the tether. This unprecedented reaction has remarkable features
that distinguish it from many other photochemical transformations:
it is particularly robust with respect to substituents, it can be
scaled up without a notable loss of efficiency, and it can lead to
structures with a high degree of complexity in low to good yields.
All photochemical precursors could be synthesized readily in three
steps. We confirmed the compatibility of the nitrogen atom in the
photocycloaddition step, which gives access to a bicyclo[2.2.2]octadiene
scaffold with two points that allow further diversification. This
reaction was scaled up to multigram quantities without erosion of
the typically high yields in photocycloadducts. Sequential deprotection
of the N- or C-terminus of bicyclic amino acids gave access to two
conformationally constrained unnatural amino acids with different
dispositions of the two anchor points