Aza-Wittig reagent

The sequence shown in Scheme 11 was more effective if the isothiocyanate was premixed with the azide, rather than added after the phosphine. Aza-Wittig reagents can undergo exchange reactions with carbodiimides ... 

Next, we see an alternative method of generating the IMP. In this method, the aza-Wittig reagent is generated from a primary amine, triphenylphosphine, triethylamine and hexachloroethane. In this case, the resultant IMP reacts with the carbonyl of an ester. Unfortunately, slight hydrolysis of the product is observed during this process. 

The majority of published work on aza-ylides concerns their applications in synthesis, and here we report a selection of contributions from this area. The Staudinger reaction is a popular route to aza-ylides and has been used to prepare a series of perfluoroalkyl-tagged aza-Wittig reagents, e.g., (68), which were generated in situ (Scheme 22), and utilised in the synthesis of 3//-quinazolidine-4-ones in a fluorous biphasic system. A method for the preparation of aza-polycyclic compounds derived from pyrrolidine, indolizidine and indole has... 

The Synthesis and Reactions of Aza-Wittig Reagents. - A computational study of the aza-Wittig reaction, by means of ab initio calculations, has been published. ... 

It has been reported that microwave irradiation can greatly reduce the time needed to prepare aza-Wittig reagents. ... 

Di- and tri-acylated imines, formed by the reaction of aldehydo- or keto-esters with aza-Wittig reagents [Ph3p=NCOR], are moderately active dieno-philes. Cycloaddition occurs with a good degree of regiospecificity, as illustrated by the example shown in Scheme 2. ... 

Some Heterocycles Formed with Aza-Wittig Reagents... 

TMSK can also react with in situ generated aza-Wittig reagents to furnish azeto[2,l-fc]quinazolines and isoquinolines (eq 20). ... 

Intermolecular aza-Wittig reaction has been described for the one-step synthesis of pyrazolofl, 5-a Ipyrimidinc and imidazo[l,2-fc]pyrazole derivatives.37 The asymmetric synthesis of ft-quaternary azacycles has been accomplished by aza-Wittig reaction mediated by chiral phosphorus(ni) reagents.38... 

Fluorous-tagged reagents are very attractive for reactions in which a stoichiometric by-product is formed that is difficult to separate. An example is perfluor-oalkylated triphenylphosphane for use in Wittig and aza-Wittig reactions, where the corresponding phosphane oxide is removed by fluorous extraction [22, 23]. Similarly, fluorous sulfoxide has been employed in Swern oxidations, and fluorous carbodiimide has been used as a coupling reagent [24, 25]. 

JOC43i>. An intramolecular aza-Wittig reaction ensues upon treatment of the azides with phosphorus(III) reagents (Scheme 65). Yields of oxazoles, including furyl- and pyridyl-substituted... 

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