Structure, Synthesis, and Properties of Some Persubstituted 1,2‐Dintroethanes. In Quest of Nitrocyclopropyl‐Anion Derivatives

Abstract

Attempts to deprotonate nitrocyclopropane led to solutions which showed strong ESR. signals (Fig. 1)and from which 1‐nitro‐ l′‐nitroso‐bicyclopropyl (3) and 1,1′‐dinitro‐bicyclopropyl (2) were isolated. The activation energy for rotation about the central C, C‐bond of 2 is estimated to be about 12 kcal/mol (1 H‐NMR. spectra in Fig. 2). In contrast, the oven‐chain analogue 2,3‐dimethyl‐2,3‐dinitrobutane (1) shows a methyl singlet down to −70° C. Low‐temperature X‐ray analyses of 1, 2, 3, and also of 1,1′‐dinitro‐bicyclobutyl (4) show that all four molecules have gauche‐conformations but reveal striking structural differences between the openchain and the cyclic derivatives (Fig. 4–6): the central C, C‐bond is long in 1 (1.575 Å), short in 2 (1.479 Å); the C, N‐bonds are long in 1 (1.549 Å), short in 2 (1.488 Å); the orientation of the nitro groups is bisected in 2 and perpendicular in 1. The crystal structure of the nitro‐nitroso compound 3 is isomorphous with that of the dinitro compound 2 and thus disordered (Fig. 15–16). The effect of the nitro group as π‐electron acceptor on the molecular conformations and bond lengths is discussed. From analysis of the anisotropic vibrational parameters of 2 the root‐mean‐square librational amplitude of the nitro groups about their C, N‐bonds is estimated to be about 5.8° at 95 K, corresponding to a rotational barrier of about 9 kcal/mol, i. e. the same order of magnitude as the NMR. estimate of about 12 kcal/mol for C, C‐rotation.

The fascinating implications of new results in gold chemistry

“…A series of tri-organophosphoniumbis(diphenylphosphino)methylides [54] and the di-tertiary phosphines derived from butadiene [55] and bicyclopropyl [56] adopt -as free ligands -ground state conformations which do not allow metal-metal contacts in their dinuclear complexes with AuCI. The former have a syn/anti conformation relative to the ylidic function (Figure 8a), and the latter two adopt the single-trans conformation (butadiene) or a form close to this extreme (bicyclopropyl) [57]. In 1:1 complexes, these conformations are retained, which is proof that phosphine coordination in principle is not necessarily associated with conformational changes.…”

Self‐Regeneration of Stereocenters (SRS)—Applications, Limitations, and Abandonment of a Synthetic Principle

“…[271] R' = H, CH3 51 % Scheme 28. In situ generation and trapping of unstable enolates [48,89] and nitronates [273,274] with aromatic aldehydes with the assistance of the aldehyde adducts A [272] and B (lithiated hemi-aminal and lithiated hemi-acetal [89], respectively); the Li derivative A is usually used for the orthometalation of aromatic aldehydes [272]. In light of the instability of the enolates formed tiom the bicyclic compound shown, we conclude that this does not result from reaction of the free LiNR,, which exists in equilibrium with A, but that deprotonation, generation of the aldehyde, and aldol or nitroaldol addition result in a "collision complex" (see for example C and the accompanying caveat in the text).…”

New reactions of γ-halocarbanions: underestimated reactive intermediates in organic synthesis

“…Due to the low nucleo philicity of the nitronate anions, only γ iodonitropropane slowly cyclizes to nitrocyclopropane when treated with a base. 12 Recently, it was reported that the γ mesyloxy nitropropane anion reacts with imines to give substituted nitropyrrolidines 13 (Scheme 10).…”