Wittig-type catalysts

The Schrock catalyst shown in Figure 16.12 does react cleanly with benzaldehyde according to the equation shown in Figure 16.21, a Wittig- type reaction [19], The compound did not react with ethyl acetate or N,N-dimethylformamide for several weeks at room temperature. 

Various carbonyl compounds, such as ( )-3-(benzyloxy)propenal (30), do not react with cyclo-propylidenetriphenylphosphorane. However, the addition of a phase-transfer catalyst can greatly influence the progress of a reaction. Thus, yields obtained from Wittig-type reactions with cyclopropylidenetriphenylphosphoranes are greatly improved by the addition of tris[2-(2-methoxyethoxy)ethyl]amine (TDA-l). The failure of ( )-3-(benzyloxy)propenal to react with cyclopropylidenetriphenylphosphorane was converted into a useful reaction when 10 mol % of TDA-1 was utilized. ... 

Di-, tri-, and tetra-substituted 2-azadienes (64) carrying electron-withdrawing groups have been synthesised by the aza-Wittig reaction. A one-pot synthesis of olefins from diorganyltelluride, diazo compounds, and carbonyl compounds in the presence of a Cu(I) catalyst is suggested to involve a Wittig-type reaction of an intermediate telluronium ylide. ... 

The cobalt(II) porphyrin complex (CoTPP) has been found to be an efficient catalyst for the Wittig type olefination of acyl phosphonates (96) with ethyl diazoacetate (EDA) in the presence of triphenylphosphine (Seheme 32). ° In a one pot reaction under mild conditions, highly functionalized vinyl phosphonates (97) could be obtained in high yields (72-92%) and high E/Z selectivities (95/5-100/0), in relatively short reaction times. 

The first attempt to use a chiral catalyst in an asymmetric Wittig-type reaction was reported in 1970 [22]. A combination of the stabilized ylide 9 and a chiral organic acid as an external catalyst was evaluated in the olefination of 4-substituted cyclohexanone derivatives 1. In this study, (S)-(+)-mandelic acid was found to be... 

The transition metal-catalyzed cyclopropanation of alkenes is one of the most efficient methods for the preparation of cyclopropanes. In 1959 Dull and Abend reported [617] their finding that treatment of ketene diethylacetal with diazomethane in the presence of catalytic amounts of copper(I) bromide leads to the formation of cyclopropanone diethylacetal. The same year Wittig described the cyclopropanation of cyclohexene with diazomethane and zinc(II) iodide [494]. Since then many variations and improvements of this reaction have been reported. Today a large number of transition metal complexes are known which react with diazoalkanes or other carbene precursors to yield intermediates capable of cyclopropanating olefins (Figure 3.32). However, from the commonly used catalysts of this type (rhodium(II) or palladium(II) carboxylates, copper salts) no carbene complexes have yet been identified spectroscopically. 

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