Homochiral α-d- and β-d-Isoxazolidinylthymidines via 1,3-Dipolar Cycloaddition

B(C6F5)3-Catalyzed Diastereoselective and Divergent Reactions of Vinyldiazo Esters with Nitrones: Synthesis of Highly Functionalized Diazo Compounds

Herein we report a mild, transition-metal-free, highly diastereoselective Lewis acid catalyzed methodology toward the synthesis of isoxazolidine-based diazo compounds from the reaction between vinyldiazo esters and nitrones. Interestingly, the isoxazolidine products were identified to have contrasting diastereoselectivity to previously reported metal-catalyzed reactions. Furthermore, the same catalyst can be used with enol diazo esters, prompting the formation of Mukaiyama-Mannich products. These diazo products can then be further functionalized to afford benzo[b]azepine and pyrrolidinone derivatives.

N-heterocyclic carbene-catalyzed rearrangements of vinyl sulfones

N-heterocyclic carbenes catalyze the rearrangement of 1,1-bis(arylsulfonyl)ethylene to the corresponding trans-1,2-bis(phenylsulfonyl) under mild conditions. Tandem rearrangement/cycloadditions have been developed to capitalize on this new process and generate highly substituted isoxazolines and additional heterocyclic compounds. Preliminary mechanistic studies support a new conjugate addition/Umpolung process involving the ejection and subsequent unusual re-addition of a sulfinate ion.

Botcinolide/Botcinin: Asymmetric Synthesis of the Key Fragments

The asymmetric synthesis of key fragments of the phytotoxic toxins botcinolide/botcinin is reported. The synthesis of 1 and 1a are based on a convergent route via esterification and alkene metathesis of fragments A, B or C, B, which were obtained by Evans aldol condensation and stereoselective crotylation, respectively.

Asymmetric synthesis of enantiopure isoxazolidinone monomers for the synthesis of β-oligopeptides by chemoselective amide ligation

The design and general synthesis of enantiopure isoxazolidinone monomers as precursors for the preparation of enantiopure N-terminal hydroxylamine-β(3)-oligopeptides, which may be used as reaction partners with α-ketoacids in the decarboxylative amide ligation reaction, is described.

Asymmetric 1,3-dipolar cycloadditions of acrylamides

This critical review, which is relevant to researchers in synthetic organic chemistry, focuses on asymmetric 1,3-dipolar cycloadditions with acrylamides. The use of chiral acrylamides as dipolarophiles leads to high levels of stereocontrol, due to conformational constraint in the acrylamides. Employment of chiral tertiary acrylamides containing nitrogen heterocycles is particularly effective in controlling the stereoselectivity. Following a general overview of 1,3-dipolar cycloadditions, the main body of the review focuses on asymmetric 1,3-dipolar cycloadditions of acrylamides with nitrile oxides, nitrones, diazoalkanes and azomethine ylides, with particular emphasis on the rationale for the observed stereocontrol (215 references).

Asymmetric multicomponent reactions (AMCRs): the new frontier

Asymmetric multicomponent reactions involve the preparation of chiral compounds by the reaction of three or more reagents added simultaneously. This kind of addition and reaction has some advantages over classic divergent reaction strategies, such as lower costs, time, and energy, as well as environmentally friendlier aspects. All these advantages, together with the high level of stereoselectivity attained in some of these reactions, will force chemists in industry as in academia to adopt this new strategy of synthesis, or at least to consider it as a viable option. The positive aspects as well as the drawbacks of this strategy are discussed in this Review.

Asymmetric Synthesis of the Azabicyclic Core of the Stemona Alkaloids

A general strategy for the construction of the 1-azabicyclo[5.3.0]decane core of Stemona alkaloids is developed. Our diversity-oriented approach exploits 1,3-dipolar cycloaddition of five-membered cyclic nitrones to C(6) olefins, followed by N-O reductive cleavage and azepine closure. The use of various enantiopure pyrroline N-oxides allows for a practical, stereoselective preparation of several putative precursors of different Stemona alkaloids.

Intramolecular cycloadditions of alpha-allyloxycarbonylnitrones: stereoselective synthesis of 3-amino-2(5H)furanones

Treatment of furoisoxazolidines with NaH leads to functionalized 3-amino-2(5H)-furanones through a new rearrangement pattern of the isoxazolidine nucleus. This process has been usefully exploited for the synthesis of enantiomerically pure (5R)-3-alkylamino-5-methyl-2(5H)-furanones.

Synthesis of a new class of 5'-functionalized adenosines using a rh(ii)-catalyzed 1,3-dipolar cycloaddition

[reaction: see text] Chemically protected adenosine was functionalized at the 5' position to generate novel dipolarophiles and mesoionic dipoles. These species were found to undergo facile 1,3-dipolar cycloaddition to afford a new series of adenosine derivatives that contain a point of diversification at the 5' position of adenosine.