S. Bertrand et al., Diastereoselective tandem addition-cyclization reactions of unsaturated tertiary amines initiated by photochemical electron transfer (PET), J ORG CHEM, 65(25), 2000, pp. 8690-8703
Polycyclic molecules and tetrahydroquinoleines were obtained in a tandem re
action involving the diastereoselective addition of or-aminoalkyl radicals
to (5R)-5-menthyloxy-2[5H]-furanone 1. The facial diastereoselectivity on 1
is greater than or equal to 90%. The alpha -aminoalkyl radicals were produ
ced from tertiary amines by photachemical-induced electron transfer. When N
,N-dialkylanilines 19 were used as starting tertiary amines, a rearomatizat
ion step was involved and important side reactions of 1 were observed. A me
chanistic study involving isotopic labeling of the starting amine indicated
that the byproducts resulted from reduction of 1 during the rearomatizatio
n process. An efficient optimization of the reaction was obtained by simply
adding acetone or cyclopentanone as mild oxidants to the reaction mixture.
The side products resulting from reduction of the furanone 1 were complete
ly suppressed under these conditions, and the yields of the tettahydroquino
lines 21a-i, 22a-f, and 26g-i were doubled.