REGIOSELECTIVE ROUTES TO NUCLEOPHILIC OPTICALLY-ACTIVE 2-CARENE AND 3-CARENE SYSTEMS

Commercially available (+)-3-carene (4) is shown to be capable of efficient conversion to vinyl bromides 28, 46, and 49 and to vinyl stannane 44. All four compounds stem from (+)-3-norcaranone (23), an optically pure ketone best prepared by epoxidation of 4, followed by oxirane ring opening, acetylation, ozonolysis, and CrCl2-promoted reduction. The strong proclivity exhibited by 23 to enolize in the cyclopropyl carbinyl sense is used to advantage to gain entry to 28 and 44. Remarkably, the tosylhydrazone of (+)-3-norcaranone (45) is distinguished from its ketone progenitor 23 by its capacity for highly regioselective deprotonation from the alternative a-position. The crossover has made possible synthetic access to 46 and 49. Other chemistry of this class of compounds is also presented, including a route to 51, a vinyl bromide epimeric to 49. Especially relevant to future work in the ingenol area is the ability of these molecules to serve as nucleophiles. Several reactions involving 28 are provided as exemplary of this property. © 1990, American Chemical Society. All rights reserved.