(8R,8aS)-Indolizidine-1-spiro-2'-(1',3'-dithiane)-8-carbonitrile

tert-Butyl (3S,6R,9R)-(5-oxo-3-{[1(R)-phenylethyl]carbamoyl}-1,2,3,5,6,7,8,8a-octahydroindolizin-6-yl)carbamate monohydrate at 95 K

“…However, we calculated the puckering parameters for the six-membered ring in these two literature structures and found them to be quite similar [Q = 0.479 and 0.531 (6) A Ê ; = 40.5 and 55.3 (5) ; 9 = 229.2 and 215.6 (8) , respectively] to those of the title compound, which are close to the ideal values for a half-chair conformation (Cremer & Pople, 1975). Hua et al (1995) state that`normally, the six-membered lactam ring assumes a distorted chair conformation owing to the tendency of the amide bond to be planar' and this is in agreement with the perfect chair conformation reported for different indolizidine moieties (Koh et al, 1993;Fleming et al, 1996;Mukhopadhyyay et al, 1998). The ®ve-membered ring adopts an almost perfect envelope conformation for the atom sequence C9ÐC1ÐC2Ð C3ÐN2; the puckering parameters are q = 0.388 (2) A Ê and 9 = 217.1 (4) (the nearest ideal value for an envelope amounts to 9 = 216 ), and atom C1 is 0.596 (4) A Ê from the mean plane de®ned by atoms C2, C3, N2 and C9 (the r.m.s.…”

“…deviation of these four atoms from their plane is 0.002 A Ê ). The same conformation has been found both in indolizidinone (Hua et al, 1995) and indolizidine (Koh et al, 1993;Fleming et al, 1996;Garofano et al, 1998;Mukhopadhyyay, 1998) systems. The two rings are trans-fused (Table 1).…”

α,β-Unsaturated Nitriles: Stereoselective Conjugate Addition Reactions

“…Stereochemical assignment of the indolizidine epimers was achieved by X-ray crystallography. Surprisingly, the major isomer 3a was found to have the nitrile group in the axial orientation. The origin for this stereochemical preference is unclear, but we note that a thermodynamic preference for the axial isomer is conceivable given the small A -value (0.2 kcal mol -1 ) for a nitrile group (vide infra).…”