1882-42-4Relevant articles and documents
Unusual conformational effect in alpha-aminoorganostannanes.
Gawley,Low,Chambournier
, p. 653 - 655 (1999)
[formula: see text] Dynamic NMR analysis of conformationally mobile and rigid 2-tributylstannyl-N-methylpiperidines revealed an unexpected conformational effect that is manifested in a small energy difference between conformers in which the tin is equatorial and axial. The major reason appears to be a distortion of the conformer in which the C-2-Sn bond is synclinal to the nitrogen lone pair.
Synthesis and reactivity of conformationally locked alpha-aminoorganostannanes and alpha-aminoorganolithiums. Discovery of a surprising configurational requirement for transmetalation.
Chambournier,Gawley
, p. 1561 - 1564 (2000)
[equation--see text] 2-Tributylstannyl-N-methylpiperidines that are conformationally locked by a 4-tert-butyl substituent were evaluated in transmetalations (Sn-Li exchange) and reactions with electrophiles. When the tin is equatorial, transmetalation occurs smoothly as does reaction with carbonyl electrophiles. Alkyl halides seem to undergo single electron transfer reactions, affording nonselective alkylation products, along with products of radical disproportionation. In a surprise, an axially oriented tin failed to transmetalate, suggesting that a synclinal relationship between the nitrogen lone pair and the carbon-tin bond is a requirement for transmetalation.
Determination of the configuration in six-membered saturated heterocycles (N, P, S, Se) and their oxidation products using experimental and calculated NMR chemical shifts
Budesinsky, Milo?,Vaněk, Václav,Dra?ínsky, Martin,Pohl, Radek,Po?tová-Slavětínská, Lenka,Sychrovsky, Vladimír,Pícha, Jan,Císa?ová, Ivana
, p. 3871 - 3886 (2014)
The six-membered saturated heterocycles - 4-tert-butyl-1-methylpiperidine, 4-tert-butyl-1-methylphosphine, 4-tert-butyl-tetrahydro-2H-thiopyran, and 4-tert-butyl-tetrahydro-2H-selenopyran - were prepared as suitable model compounds with well-defined geometry for an NMR study of their oxidation products. The corresponding epimeric N-oxides, phosphinoxides, sulfoxides, and selenoxides were obtained by standard chemical preparation and also by in situ oxidation with meta-chloroperbenzoic acid directly in the NMR tube. The experimental 1H and 13C chemical shifts were compared with corresponding calculated data obtained by GIAO approach with DFT, MP2, and HF methods and various basis sets. The correlation of experimental versus calculated data showed the possibility to determine the stereochemistry of the epimeric oxidation products using fast DFT B3LYP/6-31G* method for both geometry optimization and NMR chemical shifts calculation.
Efficient Solution-Phase Parallel Synthesis of 4-Substituted N-Protected Piperidines
Wang, Xiaoyang,Kauppi, Anna M.,Olsson, Roger,Almqvist, Fredrik
, p. 4586 - 4592 (2007/10/03)
Practical conditions for the synthesis of 4-substituted N-protected piperidines through CuCN·2LiBr-catalyzed organozinc additions to 1-acylpyridinium salts and subsequent hydrogen-transfer hydrogenation have been established. The reaction sequence is performed at room temperature and provides 4-substituted N-protected piperidines in excellent overall yields without the isolation of intermediate dihydropyridines, In those cases in which the organozinc addition results in mixtures of 2- and 4-substituted dihydropyridines, the 2-substituted isomers are efficiently scavenged with maleic anhydride and subsequently removed by a mild extractive workup with NaHCO3 (sat.). The N-acyl group can conveniently be exchanged from N-phenoxycarbonyl to N-tBoc, thus allowing orthogonal deprotection strategies. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.