The Configuration of Tricyclo [7.1.1.0^2,7]undecanes and the Stereochemistry of the Reduction of Tricyclone

Abstract

SummaryA full discussion of the configuration of tricyclo [7.1 .1.02*7]undecanes related to cis-10, lO-dimethyltricyclo [7.1.1 .02,7]undec-2-en-4-one (2), the Robinson annelation product from norpinone 1 and 3-buten-2-one is given, based on 360-MHz-NMR. spectra. Nuclear Overhauser effects confirm the cis configuration of 2, and show that the saturated ketone 10, obtained by catalytic hydrogenation, is also all-cis with the cyclohexanone ring in the boat conformation. The parent hydrocarbon, cis-10, lO-dimethyltricyclo [7.1.1 .02.7]undecane is compared with one of the corresponding trans isomers prepared from pinocarvone (14). The stereochemistry of metal hydride reduction and Grignard reaction of 2 is examined.Earlier work has suggested that 'Tricyclone"), the compound formed by Robinson annulation of 3-buten-2-one to the norpinone 1 should be ascribed the cis configuration 2 [I]. This attribution is supported by the observations of Barthklkmy & BessiBre [2] [3] who showed that under non-solvating conditions, the ions formed by addition of HBr to a-pinenes rearrange by migration of the gem-dimethyl bridge (to bornanes) in the case of cis-substitution, and of the methylene bridge (to fenchanes) in the case of trans-substitution. The hydrocarbon 3 derived from 2 rearranges to the bornane 4 under these conditions. Nevertheless, direct spectral evidence for the configuration of 2 was lacking, and we now present a full discussion of the NMR. spectra of this and related substances, and describe the stereochemistry of various reductions of 2.Base-catalyzed deuterium exchange [4] of 2 yielded mainly the tetradeuteriated compound 5, and it was possible to analyze the 360-MHz-'H-NMR. spectrum in detail (see Table I for a list of the chemical shifts of 2, 5, and other related I )Brand name of Firmenich SA.

Configurationally dependent hydroxyl group effects on 13C nuclear magnetic resonance chemical shifts of olefinic carbons in cyclic six-membered allylic alcohols

“…Cyclic six-membered allylic alcohols as a class, although common in organic synthesis as well as in the field of natural products (1,2), are of special interest since they display I3c nmr chemical shifts that are often difficult to predict and interpret, particularly in relation to the geometrical features of the molecule.…”

“…1, adhered to eq. [2]; the complete sets of parameters for both straight lines, representing the behavior of pseudoaxial and pseudoequatorial allylic alcohols, are collected in Table 2.…”

“…[2], allow the estimation of AS(sp2) for the related pseudoequatorial or pseudoaxial allylic alcohols, providing a tool for the hydroxyl group stereochemical assignment by comparison of the resonances of the olefinic carbons of the alcohol with those of the parent olefin.…”