Jesus M. Aizpurua

Asymmetric Synthesis of β-Lactams by Staudinger Ketene-Imine Cycloaddition Reaction

[2 + 2] Cycloaddition reactions between ketenes, bearing amino-, oxy-, or halo- groups, and imines are recognized as being amongst the most important and direct routes to β-lactams. Alkyl-substituted ketenes also furnished the corresponding β-lactams upon reaction with activated imines (iminoesters). In general, ketenes are generated from the appropriate acid chloride and a tertiary amine. The major or sole product of the cycloaddition is usually the cis-β-lactam, although a few exceptions showing trans selectivity are known. In this way β-lactams with a widely varying substitution pattern at the C-3 and C-4 positions of the ring are constructed stereoselectively. The diastereoselection of the cycloaddition process can be controlled with variable success from chiral groups attached to either the ketene or the imine component, or alternatively to both. This method, in turn, has proved to be valuable for the synthesis of precursors of important β-lactam antibiotics, and new successful applications can be expected in the near future.

Highly stereoselective synthesis of α-hydroxy β-amino acids through β-lactams: application to the synthesis of the taxol and bestatin side chains and related systems.

Abstract Formation of α-hydroxy β-lactams, followed chemical elaboration at C 4 and further βlactam cleavage afforded functionalised α-hydroxy β-amino acids or their derivatives in a highly stereoselective manner.

Triazolium cations: from the “click” pool to multipurpose applications

Accessing 1,2,3-triazole compounds through the copper-catalysed azide–alkyne “click” cycloaddition reaction is now a routine synthetic tool which has resulted in a huge amount of novel molecules of varied complexity bearing such heterocycles. 3-N-Alkyl-1,2,3-triazolium salts constitute an example of “post-click” chemistry arising from the “click” pool. This Focus review outlines emerging fields of application for triazolium cations, including their use as functional ionic liquids, as precursors of mesoionic carbenes, or as components of supramolecular assemblies and molecular machines.

1,8-diazabicyclo[5.4.0]undec-7-ene (dbu): An effective base for the introduction of tbutyldimethylsilyl group in organic compounds.☆

Abstract Reaction of alcohols, thiols, amines, carboxylic acids, phenols, hydroquinones, ketoesters and amides with equimolecular amounts of t-butyldimethylchlorosilane and DBU, even in solvents other than dimethylformamide affords the corresponding t-butyldimethylsilyl derivatives in high yield.

Towards the rehabilitation of the Leuckart reductive amination reaction using microwave technology

Abstract Leuckart reductive amination of carbonyl compounds was dramatically enhanced with respect to conventional heating by a specific microwave effect when the reaction was performed, under solvent-free conditions, in a monomode microwave reactor. Excellent isolated yields (up to 97%) were attained within short reaction times (typically, 30 minutes)

Triazole-Directed Pd-Catalyzed C(sp2)–H Oxygenation of Arenes and Alkenes

Selective Pd-catalyzed C(sp(2))-H oxygenation of 4-substituted 1,2,3-triazoles is described. Unlike previous metal-catalyzed C-H functionalization events, which preferentially occur at the activated heterocyclic C-H bond, the regioselective oxygenation of the arene/alkene moiety is now achieved featuring the unconventional role of a simple triazole scaffold as a modular and selective directing group.

The nef reaction on trialkylsilyl nitronates promoted by m-chloroper-benzoic acid. An efficient route to α-alkoxyketones from nitroalkanes.

Abstract Treatment of a nitroalkene with nucleophiles, followed by silylation of the resulting nitroalkane and subsequent treatment with m-chloroperbenzoic acid, provides α-functionalized carbonyl compounds in good yields.

Asymmetric synthesis of α-keto β-lactams via [2+2] cycloaddition reaction : a concise approach to optically active α-hydroxy β-lactams and β-alkyl(aryl)isoserines

Abstract The cycloaddition reaction of the Evans-Sjogren ketenes to imines, followed by α-hydroxylation of the resulting cycloadducts provides an efficient general asymmetric synthesis of α-keto β-lactams and derivatives.

Fluoride-ion mediated reaction between trimethylsilylacetonitrile and carbonyl compounds. A new synthesis of β-trimethylsilyloxy nitrites

A new way of cyanomethylating carbonyl compounds under nucleophilic catalysis is described.

A mild method for the alcoholysis of β-lactams

Abstract Ring opening reaction of N-Boc-azetidinones using alcohols is greatly enhanced by NaN3 or KCN. Extremely mild and neutral reaction conditions are described favouring the reaction with hindered alcohols and precluding epimerization of enolizable substrates.