Dithiane anions undergo intramolecular conjugate additions with R, -unsaturated nitriles when a dithiane anion is tethered to N-1 of the 3-cyano-1,4,5,6-tetrahydropyridine nucleus. 3-Cyano-1-[2-(1,3-dithianyl-2-yl)ethyl]-1,4,5,6-tetrahydropyridine (1a) and the one-carbon homologue 1b cyclize in the presence of 12-crown-4 to generate indolizidine 3 and quinolizidine 9, in which the nitrile group exhibits a strong, thermodynamic preference for the axial orientation. Oxidation of 1b provides dithiane S-oxide 10 that undergoes a highly stereoselective conjugate addition to provide crystalline quinolizidine 13. The X-ray structure of 13 is reported and corroborates our "peg-ina-pocket" principle for stereoselective conjugate additions with R, -unsaturated nitriles.

CPMAS 13C and 15N solid‐state NMR spectroscopy, as well as solution state 14N NMR spectroscopy, was used to investigate the microstructure of poly (diallyldimethylammonium chloride). The results of these studies, supported by 14N NMR studies of model compounds, were in agreement with the earlier conclusion of other workers (via solution state 13C NMR spectroscopy) that the polymer consists of a chain of five‐membered pyrrolidinium rings, A. © 1994 John Wiley & Sons, Inc.

SYNOPSISSolid-state NMR and thermal analysis techniques were used to compare the mobility of poly(viny1 butyral) (PVB) in the presence and absence of both alumina filler particles and plasticizer. The relative mobility of main-chain and side-chain carbons increases in the presence of both plasticizer and alumina as seen from an increase in the average crosspolarization rates, (T,,), and from a general decrease in the rotating frame spin-lattice relaxation rates, ' T I P .Unlike the main-chain carbons, inversion recovery cross-polarization (IRCP) data on solution cast composites show that the side-chain methyl groups in neat PVB samples are best characterized by a monoexponential cross-polarization model. However, in the presence of alumina, a fraction of the methyl groups becomes less mobile as indicated by the biexponential IRCP behavior. Polymer phase mobility also increases below the critical pigment volume concentration ( CPVC) as seen from decreasing transition temperatures using dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). This is accompanied by an increase in the rigidity of a portion of the polymer phase above the CPVC as indicated by an increase in the apparent T g , along with an increase in the mobility of another portion as indicated by the appearance of a lowtemperature DMA transition. These trends are consistent with an increase in polymer chain packing heterogeneity in the presence of alumina.

Addition of Grignard reagents to the unsaturated oxo−nitrile 10 (4-hydroxy-4-methyl-6-oxocyclohex-1-enecarbonitrile) provides conjugate addition products with virtually complete stereocontrol. Mechanistic evidence supports a chelation-controlled conjugate addition via alkylmagnesium alkoxide intermediates. Diverse Grignard reagents having sp3-, sp2-, and sp-hybridized carbons react with comparable efficiency, with even sterically demanding nucleophiles adding with complete stereocontrol. Unsaturated oxo−nitriles that are incapable of chelation afford diastereomeric conjugate addition products through an unusual boatlike transition state. Collectively, these reactions illustrate the complementary stereoselectivity of chelation-controlled conjugate additions to hydroxylated, unsaturated oxo−nitriles and stereoelectronically controlled conjugate additions to enones.