Wittig reactions with

The use of a vinylphosphonium salt as the source of the QQ fragment instead of the more commonly employed 1,2-dicarbonyl substrate is illustrated by the pyrrole synthesis in Scheme 79b (8UOC2570). A particularly interesting feature is the intramolecular Wittig reaction with an amide carbonyl group. A very useful synthesis of pyrroles depends upon the addition of the anion of p-toluenesulfonylmethyl isocyanide (TOSMIC) to a,/3-unsatur-... 

Table 10. Wittig Reactions with Trifluoromethyl Ketones...

Maleic anhydride is a convenient dienophile because of its rapid reaction with most dienes as well as its stability and ease in handling (although it is poisonous). The diene for this reaction, 1,4-diphenyl-1,3-butadiene, is readily prepared by the Wittig reaction with benzyltriphenylphosphonium chloride and cinnamaldehyde (Chapter 11, Section I). 

Because of the strongly basic conditions needed for Wittig reactions with now-stabilized ylides, one-pot reactions have not been carried out [57]. Ley s recent report of a TPAP-Wittig oxidation performed in a sequential one-pot manner is thus a promising alternative [58]. The reaction is fast and straightforward the... 

Disconnection (a2) leads to the industrial synthesis as the half aldehyde, hall ester (46) of fumarie acid (100% tpans) is available and the Wittig reaction with unstabilised ylid (45) gives 85% cis geometry in the new double bond. 

The adjustment of the oxidation level is most easily achieved by reducing the protected ester (56) to the alcohol and re-oxidising. The Wittig reaction with a stabilised ylid (55) gives mostly ff-(53). 

Using optimized reaction conditions, the Wittig reactions with four of the five aldehydes resulted in an improvement in their yields (see Figure 4.89 below) [13]. 

Scheme 13.15 Tandem Borrowing Hydrogen Wittig reaction with Ru-NHC complexes...

The carbonyl group of l-oxo-2-alkenylphosphonates (57) undergoes stereoselective Wittig reaction with acylidenephosphoranes... 

Recently, water-soluble phosphonium salts were synthesized and their Wittig reactions with substituted benzaldehydes were carried out in aqueous sodium hydroxide solution (Eq. 8.114).309... 

Because in this case an elimination reaction could occur to form an a,/ -unsaturated ester, use of two equivalents of the phosphorane should be avoided.1The (a-acylalk-ylidene)triphenylphosphorane can be subjected to a subsequent Wittig reaction with an aldehyde.[4] [5],[8]... 

The photochemical fragmentation of vinyl-substituted 1,2k5-oxaphosphetanes, representing a step of a photochemical variant of the Wittig reaction with methyl-eneoxophosphoranes, has been examined as a model in the case of 22b20). Photolysis of this compound in methanol affords the 1,3-diene 24b as well as the highly reactive dioxophosphorane 23 which is trapped by the solvent subsequent esterification of the half-ester 62, formed as a primary product, with diazomethane to give the diester 63 was undertaken solely for preparative reasons 20). 

Reaction of the tri- -butylphosphine adduct 180 with compound 157 leads to cycloaddition across the two sulfur atoms to give corresponding 2-tri- -butylphosphoranylidene-l,3-dithiole 181, which can be trapped by in situ Wittig reaction with benzaldehyde to give 182 (Scheme 21) <1994CC2603, 1997T2261>. 

Hori and co-workers accomplished the first synthesis of azathianaphthalene and azathiaphenanthrene in 1979 <79TL3969>. Their approach began with the formation of an olefin from o rt/20 -ni t ro b e n za 1 dehyde 43, via a Wittig reaction with an ylide and a subsequent reduction with zinc to afford cis and trans ortho-aminostyryl methyl sulfide 45. The cis-olefin was then treated with NCS, AgCKAi and KOH to yield 2-methyl- l-aza-2-thianaphthalene 47 in 41% yield. 9-Methyl- 10-aza-9-thiaphenanthrene 48a and 9-ethyl-10-aza-9-thiaphenanthrene 48b were obtained in a similar fashion in almost quantitative yields, whereas 6-benzyl-67/-d i b e n zo [ c, e] [ 1,2 J t h i azi n cs 50 were isolated in moderate yields via a 1,2-rearrangement (Scheme 13) <90TL7021>. 

Aminoethylidenehydrazones 161 react with triphenyl phosphine to give the azinoiminophosphorane intermediates 162 which cyclize via an aza-Wittig reaction with benzaldehydes to give the corresponding 1,2,4-triazoles 163a-j (Scheme 14 and Table 32) <2002JHC845>. 

Direct hydrogenation of key intermediate 248 over the Adams catalyst and subsequent lithium aluminum hydride reduction yielded the two stereoisomeric alcohols 256 and 257, which were separately transformed to ( )-corynantheal (258) and ( )-3-epicorynantheal (259), respectively, by Moffatt oxidation, followed by Wittig reaction with methyltriphenylphosphonium bromide and, finally, by demasking the aldehyde function (151, 152). 

Corresponding vinyl sulfides (5)7 and enamines (6)8 are accessible by the same Wittig reaction with alkyl thiotrifluoroacetates and disubstituted-trifluoroacetamides respectively. 

Wittig reaction with polymer-bound phosphonium salts... 

Scheme 19 Wittig reaction with a phosphonium ion as probase and as substrate.

A very special example is shown in Scheme 35 with the formation of bisglucosylcarbodiimides (61) from 2-azidoglucose via an aza-Wittig reaction with CO2 or CS2. Subsequent addition of water affords bisglucosyl ureas (62) (64AG227). Further examples for the syntheses of carbodiimides are presented in Section VI. 

An interesting l,3-oxazol-2-one synthesis of 126 starts from propargyl alcohol 125, CO2, and primary amines with n-butylphosphane as a catalyst (Scheme 50). It is not yet clear if the phosphane reacts by formation of an iminophosphorane followed by an aza-Wittig reaction with CO2 (90TL1721). 

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