Camphor‐Derived N‐Acryloyl and N‐Crotonoyl Sultams: Practical Activated Dienophiles in Asymmetric Diels‐alder Reactions. Preliminary Communication

Abstract

Starting from (+)‐camphor‐10‐sulfonyl chloride (5), the crystalline sultam 8 was easily prepared. Lewis‐acid‐promoted Diels‐Alder additions of the crystalline N‐acry‐loyl and N‐crotonoyl derivatives 9 and 10, respectively, to cyclopentadiene and 1,3‐butadiene at −130 to −78° furnished adducts 11, 12 and 17 with high chiral efficiency. Crystallization of the adducts and nondestructive removal of 8 gave either alcohols 13, 14 and 18 ir acid 19 in 99% enantiomeric purity. The sense of induction was reversed on using the enantiomer of 8 as the auxiliary. The structure of 10 was established by X‐ray diffraction analysis.

Least-squares absolute-structure refinement. Practical experience and ancillary calculations

“…The intensity measurements are from routine data collections made with Mo Ka radiation at room temperature on a Philips PWll00 four-circle diffractometer. Parameters refined were the scale factor, Cenzual & Parth6 (1985); DEPM, Depmeier (1985); BEDU, Bernardinelli, Dunand, Flack, Yvon, Giersch & Ohloff (1984); BEWG, Bernardinelli & Giersch (1985); H IJE and H IBO, Jefford, Bernardinelli, Boukouvalas & Higa (1985); BEDE, Berset, Depmeier, Boutellier & Schmid (1985); BEGE, Grrard, Lucken & Bernardinelli (1985); MEDE, Mendoza-Alvarez, Depmeier, Schmid & Yvon (1985b); MEAL, Mendoza-Alvarez, Depmeier, Schmid & Yvon (1985a); BEKU, Kiindig, Perret & Bernardinelli (1985); DUFL, Dunand & Flack (1983); BERN, Bernardinelli & Flack (1985); BECH, Oppolzer, Chapuis & Bernardinelli (1984a); BEKE, Oppolzer, Kelly & Bernardinelli (1984); BEOP, Oppolzer, Chapuis & Bernardinelli (1984b); BEFL, Oppolzer, Dudfield & Bernardinelli (1985); HOVE, Hovestreydt (1984); BEGI, Berdardinelli & Giersch (1985 (Stewart, Machin, Dickinson, Ammon, Heck & Flack, 1976) was used for almost all of the refinements. The x parameter converges in two cycles with one large step followed by a small adjustment even when x=0.5.…”

Stereoselectivity in the TiCl4-Catalyzed [4+2] Cycloaddition of Cyclopentadiene to (2R)-Bornane-10,2-sultam Derivatives of Fumaric Acid Monoesters

“…Thus, the diastereoselectivity observed for the endo attack on the ethyl-and benzyl-ester analogues (À)-1c,d decreases for these sterically more demanding esters 9 ). This is logical, since the p-face selectivity of this kind of dienophile is partially steric in origin [18] [25]; thus, such a trend is also observed for both endo and exo (catalyzed) [4 2] cycloaddition to (À)-1b ± d ( Entries 8 ± 10). The ester substituent may not only sterically influence the approach of the diene, but may also modify the coplanarity of the dienophile as well as its intrinsic electronic properties.…”

“…± The syntheses of crystalline (À)-1b,c were earlier reported [15] [16], while (À)-1d was obtained in 83% yield, after crystallization from CCl 4 , by addition of the corresponding crude acid chloride (fumaric acid monobenzyl ester [17], (COCl) 2 (2.0 mol-equiv. ), toluene, 808) to the deprotonated free camphorderived sultam (NaH, 1.1 mol-equiv., toluene, 0 ± 208 [18]). …”

“…The diene, thus removed from the prosthetic group, shows much lower p-facial discrimination in the exo approach 11 ). Based on earlier work [18] [25] [27] as well as on X-ray analysis of a TiCl 4 -sultam complex [26], we propose that the CC bond is conformationally s-cis-restricted with respect to the CO/SO 2 syn-chelated moieties of the sultam, thus offering its C(a)-re face to the sterically and stereoelectronically preferred endo attack [28]. In the uncatalyzed case, the same face is prone to endo addition [28] 12 ), the methoxycarbonyl group, being slightly more stable in a s-cis-conformation with respect to the reactive CC bond, may change to a s-trans conformation in case of competitive coordination with TiCl 4 .…”

“…of TiCl 4 (Entry 15), or for the sterically more demanding benzyl ester (À)-1d (Entries 10 and 13). The X-ray analysis of endo-(2R,3R)-2b (see Table 2 for selected structural parameters) exhibits the usual features of such N-acylbornane-10,2-sultams [18], such as the anti-periplanar disposition of the SO 2 /C(O) moieties, with concomitant anomeric pyramidalization of the N-atom [28] 13 ).…”