Recent advances in the chemistry of conjugated enamines

Bond Energies of Enamines

Energetics of reactive intermediates underlies their reactivity. The availability of these data provides a rational basis for understanding and predicting a chemical reaction. We reported here a comprehensive computational study on the energetics of enamine intermediates that are fundamental in carbonyl chemistry. Accurate density functional theory (DFT) calculations were performed to determine the bond energies of enamines and their derived radical intermediates. These efforts led to the compilation of a database of enamine energetics including a thermodynamic index such as free-energy stability, bond dissociation energy (BDE), and acid dissociation constant (pK _a) as well as a kinetic index such as nucleophilicity and electrophilicity. These data were validated by relating to experimentally determined parameters and their relevance and utility were discussed in the context of modern enamine catalysis. It was found that pK _a values of enamine radical cations correlated well with redox potentials of their parent enamines, the former could be used to rationalize the proton-transfer behavior of enamine radical cations. An analysis of the BDE of enamine radical cations indicated that these species underwent facile β-C-H hydrogen transfer, in line with the known oxidative enamine catalysis. The enamine energetics offers the possibility of a systematic evaluation of the reactivities of enamines and related radicals, which would provide useful guidance in exploring new enamine transformations.

Recent advances in the synthesis of benzimidazol(on)es via rearrangements of quinoxalin(on)es

The review describes all the quinoxaline-benzimidazole rearrangements as a whole and the new quinoxalinone-benzimidazol(on)e rearrangements in particular when exposed to nucleophilic rearrangements which can be used for the synthesis of various biheterocyclic motifs.

Use of sulfur fragments for the synthesis of nitrogen heterocycles

This contribution contains a representative sampling from the Padwa laboratory of the conjugate addition of oximes with 2,3-bis(phenylsulfonyl)-1,3-butadiene followed by a subsequent dipolar cycloaddition cascade to produce a variety of alkaloids. The resulting cycloadducts are cleaved reductively to provide azapolycyclic scaffolds with strategically placed functionality for further manipulation of the target compounds.

Recent advances in stereoselective synthesis of 1,3-dienes

The aim of this review is to present the latest developments in the stereoselective synthesis of conjugated dienes, covering the period 2005-2010. Since the use of this class of compounds is linked to the nature of their appendages (aryls, alkyls, electron-withdrawing, and heterosubstituted groups), the review has been categorized accordingly and illustrates the most representative strategies and mechanisms to access these targets.

Mechanisms in aminocatalysis

The mechanisms of the α-, β- and γ-functionalisations of aldehydes and α,β-unsaturated aldehydes by secondary amines are presented and discussed.

The biology and chemistry of the zoanthamine alkaloids

Marine natural products have long played an important role in natural products chemistry and drug discovery. Mirroring the rich variety and complicated interactions of the marine environment, the substances isolated from sea creatures tend to be incredibly diverse in both molecular structure and biological activity. The natural products isolated from the polyps of marine zoanthids are no exception. The zoanthamine alkaloids, the first of which were isolated over 20 years ago, are of particular interest to the synthetic community because they feature a novel structural framework and exhibit a broad range of biological activities. In this Review, we summarize the major contributions to understanding the zoanthamine natural products with regard to their isolation and structure determination, as well as studies on their biological activity and total synthesis.

Palladium catalyzed alkenyl amination: from enamines to heterocyclic synthesis

The most recent advances in the Pd catalyzed amination of alkenyl halides directed towards the synthesis of imines and enamines are reviewed. The application of this cross-coupling reaction in the synthesis of heterocycles appears to be a potentially powerful methodology. The few examples already available are also discussed.