Coupling to sp-Hybridized Carbon: 13C-13C Coupling Constants in Some Polycycloalkanecarbonitriles

Abstract

Comparison of the effect of sp-hybridized carbon on the magnitude of directly bonded and vicinal coupling constants in the labelled nitriles (1)-(7) with that of sp2 and sp3 carbon reveals some interesting, though not major, differences. As noted previously, three-bond coupling involving the labelled carbon and the bridgehead carbon in the bicyclo[n.1.1] alkanes has an important through-space component.

A Novel Rearrangement of Cyclic Glutamine Derivatives: Ring Contraction in 3,6‐Diamino‐2,3,4,5‐tetrahydropyridin‐2‐ones to Yield 5‐Iminoproline Amides

“…To obtain ester 5, N 2 -Z-l-glutamine [6] was first converted into N 2 -ZGlnOEt [7] (3, Scheme 1), and then the amide moiety in amido ester 3 was dehydrated under very mild conditions, that is, by treatment with trifluoroacetic anhydride/pyridine in dichloromethane. [8] The newly installed nitrile function in 4 played an important role in the subsequent transformations for two reasons: Compound 4 could be selectively methylated at N-2 without competitive N ω -methylation. [9] After that, the nitrile group in resulting 5 cleanly underwent the Pinner transformation, that is, conversion into imino ester 6 by treatment with hydrogen chloride in ether in the presence of ethanol (Scheme 1).…”

A New and Productive Route to 1‐Heteroarylcyclopropanols

“…Multiplicities of signals are described as follows: s ϭ singlet, d ϭ doublet, t ϭ triplet, q ϭ quadruplet, quint ϭ quintuplet, m c ϭ centrosymmetrical multiplet. Coupling constants (J) are given in Hz; J values in 13 C NMR spectra refer to 13 C-19 F couplings. EI-MS data were recorded with Finnigan MAT 95 and Varian CH 5 spectrometers (70 eV).…”

“…Conventional transformation of 12a into the acyl chloride (SOCl 2 ) and subsequent treatment with NH 3 was found to give a significantly lower yield of 13a when this reaction was carried out on a larger scale. Dehydration of the amides 13a and 13b to provide the nitriles 14a and 14b proceeded quantitatively under conditions described by Della et al [13] The subsequent two-step sequence Ϫ condensation with methyl formate and KH, followed by methylation with dimethyl sulfate Ϫ also worked well and afforded the desired building blocks 4-R. A one-pot operation without isolation of the enol 15b was found to be superior, especially when the methylation was performed in the presence of 18-crown-6. O-Methylation of the enols 15 enhances the reactivity of the α,β-unsaturated nitrile fragment towards nucleophiles.…”

Cubanes in Medicinal Chemistry

“…Compounds 9 – 19 provide multiple varied handles for incorporating cubane into larger molecules, though other building blocks have been generated, as shown in Figure . Substituted cubanes with a simple functionality, such as an aldehyde, thiol, alcohol, nitrile, and alkyne and azide moieties, have all been generated (compounds 20 – 25 , respectively). The aldehyde is best utilized in situ as it can readily decompose when isolated in pure form, and Eaton postulated that hydroxyl-substituted cubanes can readily undergo rearrangement via a ketene intermediate. , Hydroxy acid 26 , accessible from ester 10 , can also be used to generate amino acid substituted cubane 27 , while analogs 28 and 29 are accessible from 20 and 12 , respectively .…”