Begoña Lecea

On the Aromatic Character of Electrocyclic and Pseudopericyclic Reactions: Thermal Cyclization of (2Z)-Hexa-2,4-5-trienals and Their Schiff Bases

Pericyclic or pseudopericyclic? Although both mechanisms lead to the same product, they are deeply different in nature. The ring-current model proves to be a useful tool to define different kinds of aromaticity and to distinguish between pericyclic and pseudopericyclic reactions.

Surpassing Torquoelectronic Effects in Conrotatory Ring Closures: Origins of Stereocontrol in Intramolecular Ketenimine–Imine [2+2] Cycloadditions

Unexpectedand almost perfect stereochemical control is obtained in the title reactions [Eq. (a)], although torquoelectronic theory predicts negligible stereoselection. According to ab initio and DFT calculations, this stereocontrol is determined by the geometry of the first transition state of the stepwise mechanism. In good agreement with the model proposed, the presence of an additional methylene group attached to the iminic nitrogen atom promotes a significant loss of stereocontrol.

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.

N,N-Dimethylphosphoramidic dichloride: a convenient reagent for the preparation of β-lactams from acetic acids and imines

Abstract A convenient reagent for the preparation of β-lactams from acetic acids and imines is described. A new route to α-keto-β-lactams from 3-bis(ethylthio)β-lactams is also reported. Reaction of 4-acethyl-β-lactams with diazomethane is also made.

New stereochemical outcomes in the cycloaddition of acid halides or equivalents to cinnamylideneamines: A concise new approach to 4-acetoxyazetidin-2-ones.

Abstract The reaction between 2-methylcinnamylideneamines and acid halides or equivalents leads to the stereospecific formation of cis - β-lactams. A new three steps approach to 4-acetoxyazetidin-2-ones as building blocks of β -lactam antibiotics is also described.

Role of the isomerization pathways in the Staudinger reaction. A theoretical study on the interaction between activated ketenes and imidates

Abstract Theoretical studies on the Staudinger reaction between methoxyketene and a simple imidate provide an explanation for the trans stereoselectivity observed. The key step responsible for this unusual outcome is the facile interconversion between two zwitterionic intermediates through a biradical transition state.

An extension of barret's procedure for the preparation of potentially valuable carbapenem intermediates

Abstract The reaction between 4-acetoxy-N-alkyl β -lactams and enoxysilanes catalyzed by trimethylsilyl triflate is described. Application of this reaction to 4-acetoxy-N-trimethylsilylmethyl βlactams is also described.

Reagents and synthetic methods 52. Silane reduction of carbonyl compounds in the presence of iodine

Abstract Synthetic utility of 1,1,3,3-tetramethyldisiloxane (TMDS) reagent under the influence of iodine is described. TMDS reagent in combination with iodine produces alkyl iodides from carbonyl compounds and oxiranes in good to excellent yields. Reduction of quinones into hydroquinones is also described. The mentioned transformations are explained from mechanistic points of view.

An ab initio study on the mechanism of the alkene–isocyanate cycloaddition reaction to form β-lactams

Ab initio calculations predict that the [2 + 2] reaction between isocyanates and alkenes to form β-lactams is a cycloaddition which takes place through a concerted suprafacial mechanism.

A concise synthesis of 4-unsubstituted azetidin-2-ones

On catalysis by trimethylsilyl trifluoromethanesulphonate, 4-acetoxy-β-lactams react with hydrosilanes to give 4-unsubstituted-β-lactams in good to excellent yields.