Intramolecular Staudinger/aza-Wittig reaction

The intramolecular version of the tandem Staudinger/aza-Wittig reaction is often referred to as Eguchi aza-Wittig protocol (cf. references 14f, 60, 119-120, etc.)... 

Dihydroquinazolines 690 were obtained by intramolecular Staudinger -aza-Wittig tandem sequence from azides 689, which in turn were synthesized from aldehyde 688 using a four-component Ugi reaction (Scheme 144) [408]. 

The simplest available derivatives of pyrrole in this sense are pyrrolines (97) which are accessible by simple intramolecular aza-Wittig reaction of iminophosphorane 96, the latter being formed by a Staudinger reaction from -y-azidoketones (95), as shown in Scheme 44. The process occurs under neutral conditions, so that once the double bond is formed, it cannot isomerize (86TL1031 87NKK1250). 

Imidazoles are synthesized from A-(2-azidoethyl)phthalimide (136) via the Staudinger reaction to obtain an initial intermediate iminophosphorane 137, which is then converted by an intramolecular aza-Wittig reaction and... 

Treatment of thiol ester azide 212 with PPhs in anhydrous THF (under reflux) provided thiazoline 213 in good yield (Scheme 84). In situ generation of a phosphinimine by Staudinger reaction of the azide with PPh3 allowed an intramolecular aza-Wittig reaction to take place with the thioester under the neutral and anhydrous conditions <2004PNA12067>. 

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-... 

PhCH2NPPh3 affords the isocyanide derivative [Os3(CO)g(CNCH2Ph)(n3-ri rri iTi -Ceo)]. The Staudinger reaction in combination with an intramolecular aza-Wittig ring closure reaction has been applied in the synthesis of quinazolin-4-ones. Other examples of intramolecular aza-Wittig reactions are reported as parts in multi-step synthetic routes. A theoretical study of the aza-Wittig reaction of HN = PX3(X = H and Cl) with formaldehyde in the gas phase and in solution has been reported. ... 

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>. 

Progress in the synthesis of heterocyclic natural products by the Staudinger/intramolecular aza-Wittig reaction 05ARK(2)98. 

Thus, acylation of J -methylamides 38 with 2-azidobenzoyl chloride 37 (readily available from 2-azidobenzoic acid [142]) forms imides 39a-c, which upon treatment with triphenylphosphine (TPP) in the course of consecutive Staudinger reaction/intramolecular aza-Wittig reaction yield exclusively 3-methylquinazolin-4(3ff)-ones 40a-c quantitatively (Scheme 4) [143,144]. This procedure provides simple and efficient quinazoHnone annelation of amides and lactams. 

The formation of flve-membered cyclic imines through a Staudinger/intramolecular aza-Wittig reaction can also be performed by solid-phase synthesis and has been applied for the first synthesis of lanopylin Bi (108). The total synthesis, which takes only four steps, starts with a phase-transfer alkylation of diethyl 2-oxopropylphosphonate 105 with a 2-iodoethyl azide, affording the azido phosphonate 106, which undergoes a phase-transfer Homer-Emmons Wittig reaction with heptadecanal to provide the azido enone 107. An intramolecular aza-Wittig reaction of the enone 107 with polymer-supported triphenylphosphine in toluene completed the first total synthesis of lanopylin Bi (108) in 76% yield (Scheme 15.22). 

Quinazoline alkaloids containing the indole skeleton such as tryptanthrin (156) have been constructed via intramolecular aza-Wittig reaction of amide derivatives (Scheme 15.35). The fused quinazoline ring in tryptanthrin (156) could be synthesized efficiently in a one-pot procedure via the consecutive Staudinger/intramolecular aza-Wittig reaction of the corresponding azide 154 with tributylphosphine (Eguchi protocol). 

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