Decarboxylative 1,3-dipolar cycloaddition of amino acids for the synthesis of heterocyclic compounds

The [3 + 2] cycloadditions of stabilized azomethine ylides (AMYs) derived from amino esters are well-established. However, the reactions of semi-stabilized AMYs generated from decarboxylative condensation of α-amino acids with arylaldehydes are much less explored. The [3 + 2] adducts of α-amino acids could be used for a second [3 + 2] cycloaddition as well as for other post-condensation modifications. This article highlights our recent work on the development of α-amino acid-based [3 + 2] cycloaddition reactions of N-H-type AMYs in multicomponent, one-pot, and stepwise reactions for the synthesis of diverse heterocycles related to some bioactive compounds and natural products.

Catalytic Enantioconvergent Conjugate Addition of Organosilanes via a Strategy of Fluorodesilylation

Fluorodesilylation is a widely used strategy to activate organosilanes as nucleophiles for the development of organic transformations. To date, highly enantioselective catalytic fluorodesilylations have been limited to the activation of silyl ethers, organosilanes bearing specific substituents such as trifluoromethyl and cyanide, allylsilanes, and acylsilanes. However, the catalytic enantioconvergent reaction of racemic organosilanes bearing variable substituents via fluorodesilylation has been rarely reported. We report an unprecedented enantioconvergent fluorodesilylation of racemic organosilanes bearing various substituents with a chiral ammonium fluoride. Notably, these results demonstrated that the fluorodesilylation could potentially be a general strategy for the development of catalytic asymmetric reactions of racemic organosilanes.

2-Azaallyl Anions, 2-Azaallyl Cations, 2-Azaallyl Radicals, and Azomethine Ylides

This review covers the use of 2-azaallyl anions, 2-azaallyl cations, and 2-azaallyl radicals in organic synthesis up through June 2018. Particular attention is paid to both foundational studies and recent advances over the past decade involving semistabilized and nonstabilized 2-azaallyl anions as key intermediates in various carbon-carbon and carbon-heteroatom bond-forming processes. Both transition-metal-catalyzed and transition-metal-free transformations are covered. Azomethine ylides, which have received significant attention elsewhere, are discussed briefly with the primary focus on critical comparisons with 2-azaallyl anions in regard to generation and use.

One-Pot Reductive 1,3-Dipolar Cycloaddition of Secondary Amides: A Two-Step Transformation of Primary Amides

The one-pot reductive 1,3-dipolar cycloaddition of secondary aromatic N-(trimethylsilylmethyl)amides with reactive dipolarophiles is reported. The method relies on the in situ generation of nonstabilized NH azomethine ylide dipoles via amide activation with triflic anhydride, partial reduction with 1,1,3,3-tetramethyldisiloxane (TMDS), and desilylation with cesium fluoride (CsF). Running under mild conditions, the reaction tolerated several sensitive functional groups and provided cycloadducts in 71-93% yields. The use of less reactive dipolarophile methyl acrylate led to the cycloadduct in only 40% yield. A (Z) geometric intermediate of NH-azomethine 1,3-dipole was postulated to account for the observed higher yields and higher cis diastereoselectivity for the substrates bearing an electron-withdrawing group. This model features an unconventional cyclic transition state via carbanion-aryl ring interaction. Because the starting secondary amides can be prepared from common primary amides, the current method also constitutes a two-step transformation of primary amides.

A strategic approach to the synthesis of functionalized spirooxindole pyrrolidine derivatives: in vitro antibacterial, antifungal, antimalarial and antitubercular studies

A series of spirooxindole pyrrolidine derivatives has been synthesized and evaluated for theirin vitrobiological activities. The observed regio- and stereoselectivity of the cycloaddition reaction has been rationalized using DFT calculations.

Recent advances in the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides

The scope of the catalytic asymmetric 1,3-dipolar cycloaddition of azomethine ylides has been greatly expanded by the incorporation of novel types of dipolarophiles and dipole precursors. This feature article summarizes the recent development in this area.

Bis(trimethylsilyl)methylamine (BSMA): tool or toy?

Bis(trimethylsilyl)methylamine, BSMA, an original primary amine, was proven to be the source of a large variety of N-bis(trimethylsilyl)methylamino derivatives that otherwise have to be prepared indirectly. Because of the bulkiness of the bissilylmethyl group, regio- and stereoselectivities resulted in appropriated examples. Apart from the potential biological properties associated with the Si-C-N framework, these derivatives were powerful synthetic intermediates. Special emphasis was given to the chemistry of corresponding imines. Cleavage of Si—C bonds or abstraction of the methine proton afforded α-nitrogen carbanions in very mild conditions. Application of these results to the β-lactam chemistry allowed the introduction of new synthetic methodologies in this field. It results the (Me3Si)2CH- group could now be regarded as a Me3SiCH2- or a CH3- group or a proton equivalent.Key words: bis(silyl)methylamine, preparations, reactivity, nitrogen heterocycles, α-nitrogen carbanions.