1, 3-dipolar, nonstabilized azomethine ylides

Dipolar cycloaddition reaction of benzo(A)thiophene-l,1-dioxide 282 with nonstabilized azomethine ylides gave high overall yield of new pyrrolo derivatives 5 and 6 with low stereoselectivity (Scheme 50) <2006TL5139>. 

A 1,3-dipolar cycloaddition of the nonstabilized azomethine ylide 6 is the key step in a three-component reaction. The azomethine ylides were generated from (2-azaallyl)stannanes or (2-azaallyl)silanes 5 through an intramolecular iV-alkylation/demetallation cascade. The ylides underwent cycloaddition reactions with dipolarophiles yielding indolizidine derivatives 7-9 <2004JOC1919> (Scheme 1). 

The 1,3-dipolar cycloaddition of diazomethane with tert-butyl 4-oxo-6-phenyl-4//-pyran-3-carboxylate 411 has been reported to give 412 (Scheme 68) <1991JOC4963>. Further development of simple 7-pyrones as the 2rt-component in 1,3-dipolar cycloadditions of stabilized and nonstabilized azomethine ylides has provided some interesting polycyclic heterocycles such as 413-415 (Scheme 68) <1999J(P1)1167>. 

The preparation of pyrrolidines has received extensive attention by synthetic chemists in recent years, in part due to the interesting biological activities exhibited by several polysubstituted pyrrolidines. Little attention has been given to one of the most conceptually simple ways of pyrrolidine formation a 1,3-dipolar cycloaddition of an azomethine ylide with an olefin. This is not surprising since few methods exist for the preparation of nonstabilized azomethine ylides. " Silyl-substituted amines of Type 1 represent conjunctive reagents which can be considered as the equivalent of a nonstabilized azomethine ylide. These reagents have recently been found to... 

CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Dennis P. Curran. Steiic Course and Mechanism of 1,3-Dipolar Cycloadditions, Rolf Huisgen. Nonstabilized Azomethine Ylides, Edwin Vedejs. Molecular Rearrangements Occurring from Products of Intramolecular 1,3 Dipolar Cycloadditions Synthetic and Mechanistic Aspects, Arthur G. Schultz. Dipolar Cycloadditions of Nitrones with Vinyl Ethers and Silane Derivatives, Philip DeShong, Stephen N. Lander, Jr., Joseph M. LeginusandC. Michael Dickson. The Cycloaddition Approach to b-Hydroxy Carbonyls An Emerging Alternative to the Aldol Strategy, Dennis P. Curran. Index. 

A series of novel dispirooxindolecyclo[pyrrolo[l,2-c]thiazole-6,5 -thiazolidine] derivatives (172) were obtained regioselectively by the 1,3-dipolar cycloaddition reaction of 5-arylidene-2-thioxothiazolidin-4-ones (171) as dipolarophiles with nonstabilized azomethine ylides, generated in situ via decarboxylative condensation of isatin (155) and thiazolidine-4-carboxylic acid (170) in ethanol under both classical refluxing and ultrasound irradiation (Scheme 8.54). Because of the advantages of ultrasonic irradiation of mild reaction conditions, short reaction times, and high efficiency, it is quite profitable to develop the 1,3-dipolar cycloaddition of azomethine ylides under these conditions (Hua et al. 2012). 

---