Synthesis, Molecular Structure, Conformational Analysis, and Chemical Properties of Silicon-Containing Derivatives of Quinolizidine

Abstract

A silicon analog of quinolizidine 3,3,7,7-tetramethylhexahydro-1H-[1,4,2]oxazasilino[4,5-d][1,4,2]oxazasilin-9a-yl)methanol 3 was synthesized. X-ray diffraction analysis confirmed the trans configuration and low temperature NMR spectroscopy both the flexibility (barrier of interconversion 5.8 kcal mol(-1)) and the conformational equilibrium (chair-chair and chair-twist conformers) of the compound. The relative stability of the different isomers/conformers of 3 was calculated also at the MP2/6-311G(d,p) level of theory. Intra- and intermolecular hydrogen bonding in 3 and the appropriate equilibrium between free and self-associated molecules was studied in solvents of different polarity. Both the N-methyl quaternary ammonium salt and the O-trimethylsilyl derivative of 3 could be obtained and their structure determined.

Silacyclohexanes, Sila(hetero)cyclohexanes and Related Compounds: Structure and Conformational Analysis

“…X-Ray analysis proved the trans,trans-fused structure in the crystal (Figure 14), but the molecule was conformationally flexible and the barrier for interconversion of the conformers was only 5.8 kcal/mol [70]. Such a flexibility might be suggestive of the cis-fused structure of the two rings in solution, because in decalin the ring inversion is possible only in the cis-isomer, whereas the structure of the trans isomer is rigid.…”

“…X-Ray analysis proved the trans,trans-fused structure in the crystal (Figure 14), but the molecule was conformationally flexible and the barrier for interconversion of the conformers was only 5.8 kcal/mol [70]. X-Ray analysis proved the trans,trans-fused structure in the crystal (Figure 14), but the molecule was conformationally flexible and the barrier for interconversion of the conformers was only 5.8 kcal/mol [70]. 9a-yl)-methanol by condensation/cyclization of 2-amino-2-(hydroxymethyl)propane-1,3-diol with ClCH2SiMe2OMe.…”

“…Among the investigated Si,N,O-heterocycles, an interesting object was the silicon analogue of quinolizidine, oxaazasilin-9a-yl)methanol, which was prepared by the reaction of aminoalcohol H2NC(CH2OH)3 with (chloromethyl)(methoxy)dimethylsilane [70] (Figure 13). X-Ray analysis proved the trans,trans-fused structure in the crystal (Figure 14), but the molecule was conformationally flexible and the barrier for interconversion of the conformers was only 5.8 kcal/mol [70]. X-Ray analysis proved the trans,trans-fused structure in the crystal (Figure 14), but the molecule was conformationally flexible and the barrier for interconversion of the conformers was only 5.8 kcal/mol [70].…”

“…Quaternization of the nitrogen atom prevents N-inversion and the isomeric ammonium salts do not suffer interconversion. When treated with methyl iodide, 9а-R-substituted quinolizidines almpost quantitatively give the corresponding salts ( Figure 16) existing as the cis/trans isomeric mixtures, in which the molar fraction of the trans isomer decreases in the following order: H > CN > CH3 > CH2OH > CH2NO2 [70].…”

“…Quaternization of the nitrogen atom prevents N-inversion and the isomeric ammonium salts do not suffer interconversion. When treated with methyl iodide, 9a-R-substituted quinolizidines almpost quantitatively give the corresponding salts ( Figure 16) existing as the cis/trans isomeric mixtures, in which the molar fraction of the trans isomer decreases in the following order: H > CN > CH 3 > CH 2 OH > CH 2 NO 2 [70]. Such a flexibility might be suggestive of the cis-fused structure of the two rings in solution, because in decalin the ring inversion is possible only in the cis-isomer, whereas the structure of the trans isomer is rigid.…”