Bornane

Abstract: The readily available enantiomers of bornane[ 10,2]sultam serve as efficient, versatile and practical chiral auxiliaries. A selection of highly r-face-selective reactions of their N-enoyl derivatives (Diels-Alder additions, dihydroxylations, 1,4-additions) as well as of their 0-metalated N,O-ketene acetals (aldolizations, alkylations, brominations, "aminations") are described. Applications to the syntheses of natural products and, particularly, of enantiomerically pure a-amino acids demonstrate their preparative potential. The abundance, crystallinity and manifold transformations of camphor (+)-L (Scheme 1) have attracted considerable interest throughout the history of organic chemistry. By means of various rearrangements and functionalizations at C(3), C(5), C(8), C(9) and C(lO), as well as cleavage of the C(l)/C(2) and C(2)/C(3) bonds, camphor has served as a fascinatingly versatile starting material for the syntheses of enantiomerically pure natural products. This chemistry, which entails incorporation of the camphor topicity into the target molecules, has been reviewed (ref. 1). Scheme 7 I Nu' I (+I 1 (4 1 (+) -Camphor (-) Camphor Here we address the issue of non-destructive chirality transfer from derivatives of (t)and (-)-camphor which serve as covalently bound auxiliary groups. Particularly, the venerable C(lO)-sulfonation of camphor, combined with the conformational rigidity of the bornane skeleton have spawned the most successful development of this field. Thus, bornane10,2-sultam (-)-J and its antipode (t)-2, accessible from inexpensive (t)and (-)camphorsulfonic acids in two simple operations were introduced in 1984 and rank today among the most practical auxiliaries (Scheme 2) (ref. 3). Both chirophore enantiomers are commercially available in kg-quantities (ref. 3c).