Aza- -Wittig

With linear immophosphoranes and alkyltdenephosphoranes, polyfluorinated ketones readily undergo aza-Wittig and Witlig reactions, respectively [5] In these caseSr the-(2+2] cycloadducts [49, 50, 122] are usually not isolated, instead. 

The aza-Wittig rearrangement in synthesis and transformations of N-hetero-cycles 97S497. 

Another total synthesis used the rich chemistry of iminophosphoranes (95AHC159). The /3-(3-indolyl)vinyl iminophosphorane 354 underwent an aza-Wittig/electrocyclic ring closure reaction to give the carboline 355 which was hydrolyzed with lithium hydroxide (Scheme 106). A selective reduction, deprotection, decarboxylation and diazotation followed by ring closure gave Fascaplysine (353) (94TL8851). 

Phenylcyclopent[c]azcpine (33a) and 6,7-fused cyclopentazepines 33b-d are formed in moderate yields in a one-pot, two-stage process involving initial condensation of triphenyl-[(l-phenylvinyl)imino]phosphoranes 32 with 6-(dimethylamino)fulvene-2-carbaldehyde (30), followed by an intramolecular aza-Wittig reaction of the iminophosphorane with the pendant aldehyde function.5 The method fails with the unsubstituted vinylphosphorane 32 (R1 = R2 = H). 

Two intramolecular aza-Wittig reactions leading to 1,3-benzoxazepines have been described. In the first,19 ethyl (Z)-3-(2-acyloxyphenyl)-2-azidoprop-2-enoates 1 are treated with triphenyl-phosphane under argon at 20°C for 3-4 hours when 2-substituted ethyl 1,3-benzoxazepine-4-carboxylates 2 are obtained in 85-90% yield. 

The tricyclic 1,3-diazepines 3 are formed by the action of two molar equivalents of aromatic isocyanates on the bis(imino-A5-phosphane) 1 in toluene at 20 C for 16 hours in a tandem aza-Wittig [2 t 2]-cycloaddition reaction . No further details were reported.167... 

Alkoxy-3//-l,4-benzodiazepin-5(4//)-ones by Intramolecular Aza-Wittig Reactions... 

An intramolecular aza-Wittig reaction of the imino-A5-phosphancs 4, prepared by the action of triphenylphosphane on the corresponding azido compounds, affords l//-l,2,4-benzo-triazepines 5.346 The reactions were carried out by heating compounds 4 in acetonitrile or 2-hydroxyethyl methyl ether for the time indicated. No further details were reported. 

The ready synthesis of iminophosphorane 767 from 766 and its subsequent conversion to benzylidene derivative 768 and aza-Wittig reaction... 

A new approach to indoloquinohne alkaloids from Cryptolepis sanguino-lenta has been reported based on the cyclization of an o-substituted vinyl isocyanate 244 imder microwave irradiation and further additional cyclization based on an Aza-Wittig reaction carried out in the presence of microwaves [159]. The apphcation of this synthetic scheme to the synthesis of Cryptotackienine 247 is reported in Scheme 91. 

The aza-Wittig reaction of phosphazenes 3 with a,P-unsaturated aldehydes gives 3-azatrienes, which on heating are converted to pyridines 4 <96TL(37)6379>. 

The synthesis of pyrrolo[3,4-c]pyridazines 20 is achieved by intramolecular aza-Wittig reactions of the phosphazines 19 <95JHC1457>. 

Sigmatropic rearrangements of anions of (V-allyl amines have also been observed and are known as aza-Wittig rearrangements.291 The reaction requires anion stabilizing substituents and is favored by (V-benzyl and by silyl or sulfenyl substituents... 

Of note, Quintela and coworkers used a related aza-Wittig/l,5-electrocydic ring-closure process to obtain access to multiheterocydic structural elements such as py-... 

In the construction of C=N bond-containing compounds, such as nitrogen heterocycles, the aza-Wittig methodology has received increased attention as the method of choice [7]. Thus, an easy access to optically active (-)-vasicinone (7-15), a pyr-rolo[2,l-fc]quinazoline alkaloid which is used in indigenous medicine [8], was... 

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-... 

Scheme 7.6. Synthesis of (-)-vasicinone (7-15) by a domino Staudinger-reduction/aza-Wittig reaction.

Scheme 9.9. Staudinger/aza-Wittig/Ugi (SAWU-3CR)-process producing N-heterocycles.

Staudinger reduction/aza-Wittig/Ugi three component reaction... 

Annulation of pyridine to indole is accomplished by a tandem aza-Wittig/electrocyclization strategy as shown in Eq. 10.68."... 

An aza-Wittig reaction-cycloaddition reaction sequence was utilized for the synthesis of pyridotriazines 94. Treatment of iminophosphorane 92 with phenylisocyanate leads to the formation of the corresponding carbodiimide intermediate, which with another molecule of isocyanate affords 94 in [4+2] heterocycloaddition reactions (Equation 13) <1997T16061>. 

Ene-nitrile oxidoisoquinolinium betaine 131 was readily prepared from vinyl triflate aldehyde 79 (Scheme 1.14). Palladium-catalyzed cyanation of vinyl triflate 79 with Zn(CN)2 in DMF at 60 °C produced ene-nitrile aldehyde 129 in 85 % yield [54]. Using the previously developed Staudinger-aza-Wittig reduction sequence, aldehyde 129 was coupled with cyclic ketal azide 121 to afford a 79 % yield of amine 130. The cyclic ketal amine 130 was then treated with 9 1 mixture of CH2CI2/TFA to provide ene-nitrile oxidoisoquinolinium betaine 131 in 93 % yield. 

NaBH(OAc)3 Staudinger reduction followed by aza-Wittig reaction, then reduction... 

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