B. Barker et al., INTRAMOLECULAR [4-CYCLOADDITION OF A PHOTOGENERATED O-QUINONE METHIDEIN AQUEOUS-SOLUTION(2]), Journal of photochemistry and photobiology. A, Chemistry, 104(1-3), 1997, pp. 91-96
Using an appropriately substituted o-hydroxybenzyl alcohol precursor 5
, it is shown that a photogenerated o-quinone methide can undergo effi
cient intramolecular [4 + 2] (Diels-Alder) cycloaddition in aqueous CH
3CN solution at 15 degrees C, to generate the hexahydrocannabinol ring
system 11. The dienophile tether must be sufficiently electron rich,
having at least three alkyl groups. Laser flash photolysis studies sho
w the intermediacy of an o-quinone methide (h(max) approximate to 400
nm) which has a lifetime > 2 ms. Quantum yields for reaction and fluor
escence parameters are also reported which depend strongly on the prop
ortion of water in the H2O-CH3CN solvent mixture. (C) 1997 Elsevier Sc
ience S.A.