Synthetic plant growth regulators. VI. The partial synthesis of optically active (4β,15α)-18-Norkaurene-15-carboxylic acids from (4β)-18-norkauren-3-one by means of a pyrrolidinium ylide rearrangement

Abstract

(4β)-18-Norkaur-16-en-3-one (4a) was alternatively acetalized (ethanediol/Dowex resin) or deoxygenated (tosylhydrazine/sodium borohydride); allylic bromination (N-bromosuccinimide) of the products, followed by alkylation of pyrrolidine gave primary allylic amines which were quaternized with chloroacetonitrile. Potassium t-butoxide-induced [2,3]-sigmatropic rearrangement, followed by acidic hydrolysis and Jones oxidation, gave respectively (4β,15α)-3-oxo-18-norkaur-16-ene-15- carboxylic acid (10a) and (4β,15α)-18-norkaur-16-ene-15-carboxylic acid. Reductions of (4a) and (10a) gave, with K-Selectride, axial (3β)- alcohols and, with sodium borohydride, mainly equatorial (3α)-alcohols. Details of a related conversion of (+)-phyllocladene into (15α)- phyllocladene-15-carboxylic acid are also recorded.