ChemInform Abstract: CONFORMATION OF 3,7‐DIAZABICYCLO‐(3,3,1)NONANES

First 1H NMR observation of chair–boat conformers in bispidinone system. Molecular structure of 3,7-diisopropyl-1,5-diphenyl-3,7-diazabicyclo-[3.3.1]nonane-9-one

“…On this basis, we also suggest the conformational type 3 for several new bispidinones (R = Et, Pr i , CH 2 CH 2 OMe, 2-furylmethyl, CH 2 CH 2 CH 2 OEt). Here we report that our rationale is unambiguously confirmed by dynamic 1 H and 13 C NMR spectroscopic studies and crystal structure investigation in the case of N,N'-diisopropylsubstituted diphenylbispidinone 4. † In the 13 C NMR spectra of 4 below -74 °C, the peak that at room temperature corresponds to the resonances of four methylene carbons splits into a pair of broadened signals of equal intensity (labelled C a and C b , see below), which are separated by 6.6 ppm at -100 °C.…”

“…Here we report that our rationale is unambiguously confirmed by dynamic 1 H and 13 C NMR spectroscopic studies and crystal structure investigation in the case of N,N'-diisopropylsubstituted diphenylbispidinone 4. † In the 13 C NMR spectra of 4 below -74 °C, the peak that at room temperature corresponds to the resonances of four methylene carbons splits into a pair of broadened signals of equal intensity (labelled C a and C b , see below), which are separated by 6.6 ppm at -100 °C. The signal related to the carbons of the isopropyl methyl groups also splits into two peaks at 17.56 and 17.04 ppm, while that related to the methine carbons is broadened.…”

“…The obtained data allow us to assume tentatively that H a , H c and C a belong to a chair ring while H b , H d and C b are assigned to a boat ring. Indeed, the literature data prove that the lowfield signals in the 13 C NMR spectra of the natural sparteinic alkaloids correspond to the rings of the boat conformation. 16 It was also established that in the 1 H NMR spectrum of sparteine, which exists in a CB conformation, the signal of the equatorial proton of the ring in the chair conformation is downfield shifted as compared to that in the boat conformation.…”

“…11,12 Whereas the conformational effects in 1,5-diphenylbispidinones in the solid state have been extensively studied by X-ray diffraction techniques, there is little work devoted to their conformational behaviour in solution. In the mid 1970's, dipole moment investigations of 1,5-diphenyl derivatives led Scheiber and Nador to the assumption that in solution these compounds undergo a degenerate chair-boat boat-chair (CB BC) interconversion 13 (Scheme 1). Studying variable temperature 13 C NMR spectra of 3 (R = Me, CH 2 Ph, Ts) revealed the same conclusion.…”

“…In the mid 1970's, dipole moment investigations of 1,5-diphenyl derivatives led Scheiber and Nador to the assumption that in solution these compounds undergo a degenerate chair-boat boat-chair (CB BC) interconversion 13 (Scheme 1). Studying variable temperature 13 C NMR spectra of 3 (R = Me, CH 2 Ph, Ts) revealed the same conclusion. 1,9,14 In the case where R = Me different values of the free activation energy ∆G ¹ (9.7 kcal mol -1 and 8.7 kcal mol -1 in refs.…”