Wittig process, aza

Recently, the same procedure has been used by Williams and coworkers in their approach to the natural product (-)-stemonine (7-18) [10], an alkaloid which exhibits broad biological activity [11]. Conversion of the formyl azide 7-16 in a Staudinger reaction with ethyldiphenylphosphine first generated a phosphineimide which was used for the subsequent aza-Wittig process (Scheme 7.7). The furnished seven-... 

Particularly notable modifications of the fundamental Wittig reaction are those described as a phospha-Wittig process (as illnstrated in equation 18) and the aza-Wittig process (as illnstrated in equation 19) and useful for the preparation of secondary amines. ... 

Quinazolines have also been prepared by the reaction of a polystyrene-bound phosphoranimine and isocyanates, followed by an intramolecular cyclization of the carbodiimide intermediate 4-Ferrocenylidene-l-aminoimidazolone derivatives have been obtained from p-ferrocenyl-a-azidoacrylates and isocyanates followed by condensation of the resulting carbodiimidoester with hydrazines " In a Staudinger/ aza-Wittig process and in the presence of PPh3, bimetallic ferrocenyl oxazole derivatives (23) - (26) have been formed by the reaction of a-... 

A new synthesis of 2-imidazolin-5-ones (194) utilizes an intramolecular aza-Wittig reaction. Readily available azidoimides are treated with triphenylphosphine to give (194) by sequential Staudinger and intramolecular aza-Wittig processes (Scheme 130) <89T6375>. 

Pyrazolopyridinium salts arise from the reactions of acylchlorides and triazolopyramidines are available from analogous reactions. Several pyridine syntheses utilize the aza-wittig process. Thermolysis of molecules with vicinal... 

Staudinger reaction (phosphazene synthesis and reactions with a special focus on the aza-Wittig process)and reviews of the applications of the aza-Wittig reaction to heterocyclic... 

Heterocyclic chemistry, of course, abounds with compounds containing C-N bonds, and the intramolecular aza-Wittig process has been adapted to form a great variety of such compounds, as indicated in the review of MoMna and Vilaplana. ... 

Here, we will review a few examples taken from the literature to demonstrate the versatility of the intramolecular aza-Wittig process in forming some common ring systems. Many other syntheses are known. Note the following characteristics (1) ester and amide carbonyls can be used in the reaction with the iminophosphorane, (2) many reactions are general with various groups attached to phosphorus, (3) iminophos-phoranes can be formed from trialkyl phosphites ((RO)3P) as well as tertiary phosphines (R3P), and (4) many reactions are so rapid that they occur at room temperature on mixing the reactants. 

In the reactions of iminophosphoranes with carbonyl and unsaturated compounds, both normal and abnormal aza-Wittig processes can be observed. Thus, the tandem aza-Wittig reaction of the iminophosphorane (6 with isocyanate or CS2 generated the 3,5-dthydro-6/f-imidazo[l,2-6]-l,2,4-triazol-6-ones in satisfactory yields, and the vinyl iminophosphorane (6 was transformed by normal aza-Wittig reactions to carbodiimides (as part of the synthetic route to 3,5-dihydro-6//-imidazo[l,2-i)]-l,2,4-triazol-6-ones). By contrast, a re-examination of the reaction of the iminophosphorane (67) with the aromatic isocyanate PhNCO showed that it gives an unexpected mixture of carbodiimides." In another example (Scheme 5), the... 

Ph3P in anhydrous THF effected thiazoline formation by the intramolecular Staudinger-aza-Wittig process to deliver C35 0-TBS ether 110. Completion of the total synthesis of the cyclodepsipeptide apratoxin A (111) from thiazoline 110 would have required only two further operations amide formation between proUne amine and /so-leucine carboxyl-ate residues and removal of the C35 0-TBS-protecling group (Scheme 15.23). 

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