Wittig reagent for preparation

Wittig reagent for preparation of (9,0-d ichloro-/>-dim ethylamino-styrene, 46,33... 

Wittig reagent, for preparation of 1,4-di-phenyl-1,3-butadiene, 40, 36 for preparation of methylenecyclo-hexene, 40,66... 

Step 1 The diol E must be protected (acetal, in this example) for the Wittig reaction to proceed. The Wittig reagent is prepared from the phosphonium iodide using sodium dimsylate, NaCH2S(0)CH3. 

The synthesis is necessarily long and we shall concentrate on the tandem aspects. The three enantiomerically pure starting materials were the acetylenic silane 135 for C-6, prepared by resolution (chapter 22), the epoxide 136, for C-l and 2, prepared from proline (chiral pool strategy, chapter 23) and the Wittig reagent 137, prepared from ethyl lactate (chiral pool again), for C-ll. 

A new procedure for the elaboration of benzylisoquinolines has been developed. Treatment of 6,7-dimethoxy-l-chloroisoquinoline with the Wittig reagent (16) prepared from veratryl chloride and tri-n-butylphosphine furnished, after workup, a 74% yield of papaverine. 

The acylation of Wittig reagents provides the most convenient means for the preparation of allenes substituted with various electron-withdrawing substituents. The preparation of o-allenic esters has been accomplished by the reaction of resonance-stabilized phosphoranes with isolable ketenes and ketene itself and with acid chlorides in the presence of a second equivalent of the phosphorane. The disadvantages of the first method are the necessity of preparing the ketene and the fact that the highly reactive mono-substituted ketenes evidently cannot be used. The second method fails when the a-carbon... 

Much better known are the fluonnatedphosphoranes, which have been widely used m the Wittig reaction for the preparation of fluoroolefms Difluoromethylena tion reactions have been effected by using a variety of conditions Treatment of dibromodifluoromethane with two equivalents of tns(dimethylammo)phosphine m carefully dried tnglyme yields a solution of bromodifluoromethylphosphonium broomide, which very effectively converts ketones to difluoromethylene derivatives A more sensitive reagent is prepared by the addihon of two equivalents of the phosphine to the reaction mixture of fluorohalomethane and a carbonyl compound [39, 40] (equation 40) (Table 14)... 

Aldehydes can be prepared by the Wittig reaction using (methoxymethylene)-triphenylphosphorane as the Wittig reagent and then hydrolyzing the product with acid. For example,... 

Triphenylmethylphosphonium bromide, preparation for use to prepare Wittig reagent (methylenetri-phenylphosphine), 40, 66... 

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