105. Photochemical transformations. Part VII. Stereospecificity in an irradiation process

Abstract

Irradiation of dehydrolumisteryl acetate affords a stereoisomer of photodehydroergosteryl acetate. By comparison of a model diene-dione from artemisin with the diene-dione obtained earlier from photodehydroergosterol it has been shown that the photochemical transformation of dehydroergosterol proceeds with inversion of configuration a t the angular methyl group. A complete stereochemical representation of photodehydroergosterol is thus provided.The solvolysis rates of tetrahydrophotohydroergosterol toluene-psulphonate and related compounds have been measured and the vinylcyclopropane ring thus shown to participate strongly in the reaction.A preliminary account of this work has already been published.1THE conversion of dehydroergosteryl acetate (I) into its photo-isomer (11; R = Ac) was described in an earlier paper of this series.2 The stereochemistry of the product (11) is

Photochemical Transformations. XVI.1 The Structure of Photolevopimaric Acid2

“…The mother liquor was concentrated and cooled to yield an additional 8 g. (10.7%) of amine salt. The combined materia] was recrystallized twice from methanol; yield 22 g. (29.6%), m.p. 178-181°( rapid heating), [«)23d +53°(c 1.50, ethanol).…”

“…of 5% aqueous sodium hydroxide in 7 ml. of methanol was stirred for 22 hr. under a nitrogen atmosphere.…”