Synthesis of a Six-Membered-Ring (2R)-10a-Homobornane-10a,2-sultam and Structural Comparison with Oppolzer×s, Lang×s, and King×s Sultams by Anna Pia Œtek a ), Christian Chapuis* b ) 1 ) and Janusz Jurczak* a ) b ) a )Department of Chemistry, University of Warsaw, Pasteura 1, PL-02-093 Warsaw b )Institute of Organic Chemistry, Polish Academy of Science, Kasprzaka 44/52, PL-01-224 Warsaw The new six-membered-ring (2R)-10a-homobornane-10a,2-sultam ()-3a was synthesized and its X-ray structural analysis was compared with that of the novel structure of the five-membered-ring (2R)-bornane-10,2- sultam analogues ()-1a,b as well as with that already published for the six-membered-ring trans-decalin-like sultam 4a. Based on DN** density-function calculations and X-ray crystallographic studies of the N-methylated analogues ()-1e and 4b and by comparing with the conformation of the N-fluoro derivatives ()-1c and()-1d, the anomeric stabilization was estimated to be smaller than the 2.0±2.5 kcal/mol earlier suggested. The direction of pyramidalization is rationalized in terms of H-bond and steric and electronic interactions and extended to the known toluenesultam derivatives 10a ± c. Introduction. ± Owing to its ready availability in both antipodal forms as well as to the crystallinity imparted to its derivatives, the tricyclic five-membered-ring (2R)- bornane-10,2-sultam ()-1a [1] has found wide application in various asymmetric methodologies and syntheses [2]. Its ability to generally induce high diastereoselec- tivity at the C(a)-atom of N-(a,b-unsaturated acyloyl) derivatives was rationalized by Kim and Curran on the basis of a steric argument, in which the approach is directed by the C(3) substituent in the chelated syn-s-cis conformation or by the pseudo-axial O(1) S substituent for the nonchelated anti-s-cis conformer [3]. Thus, this prosthetic group was compared to a masked C 2 -symmetrical form of (2R,5R)-2,5-dimethylpyrrol- idine. Based on results from [4  2] cycloadditions [4][5] or syn-dihydroxylations [6], we later completed this steric model by hypothesizing the concurrent high reactivity of the syn-s-cis conformer under uncatalyzed conditions [4]. In this same work, we also introduced the matching or mismatching stereoelectronic influence of the N lone pair (lp) on the LUMO p-facial atomic coefficients of the C(a)/C( b) reacting centers. In addition, by comparing structurally analogous dienophiles derived from ()-1a and ()-2a [7], we also demonstrated that the anti-s-cis vs . anti-s-trans equilibrium, hence the global diastereoselectivity, were strongly influenced by the pseudo-equatorial O(2) S substituent. We invoked the generalized anomeric effect [8] to rationalize the orientation of the N lp as well as its stereoelectronic influence on both the C(a)/Cb) p- system and syn/anti conformational stabilization of the dienophiles [9] 2 ). Helvetica Chimica Acta ± Vol. 85 (2002) 1973 1 ) Present address: Firmenich SA, R & D Corporate Division, P.O. Box 239, CH-1211 Geneva 8. 2 ) For N lp through-bond and through-space directing interactions, initially suggested by M¸ller and Eschenmoser, see [10a]. For nonexhaustive more recent examples, see [10b ± g]. Cieplak also proposed a hyperconjugative influence of the N lp on the incipient bond-formation through the intermediacy of a sp 2 atom, see Schemes 85 and 86 as well as reference 105 in [11].