1,3-Dipolar addition of diazomethane to 1-acetoxy-2-hydroxycyclo-hexa-3,5-diene. Synthesis of a couple of chiral ?1-pyrazolines

The 1,3-dipolar addition of diazomethane to (1R)-acetoxy-(2S)-hydroxy-3,5-hexadiene 2 takes place with complete facial selectivity to give two diastereoisomeric ?1-pyrazolines, 3 and 4, in a 3:1 ratio. This is the first example of this type of reaction on a cyclohexa-3,5-diene-1,2-diol derivative. Photochemical decomposition of 3 affords the cyclopropyl derivative 7, which retains the stereochemistry of the parent compound.