Vinyltriphenylphosphonium bromide

The reaction of triphenylphosphine hydrobromide with phenylpropiolic acid gives a mixture of the )- and (Z)-isomers of 2-carboxy-l-phenyl-vinyltriphenylphosphonium bromide (67), not just the (Z)-isomer as previously reported. ( )-2-Ethoxycarbonyl-l-phenylvinyltriphenylphos-phonium bromide (68) can be prepared in a similar reaction from ethyl phenylpropiolate. 

Additions to Vinylphosphonium Salts. Vinyltriphenylphosphonium bromide reacts with the enolate (141) to give a one-stage synthesis of the tricyclic ketone (142) (Scheme 6).135... 

In vinylic phosphonium salts, the jft-carbon is found to be substantially deshielded (A<5 = 22.4 ppm for the vinyltriphenylphosphonium bromide as compared with ethylene), although only a small inductive effect was expected. The extent of this was interpreted to be a consequence of pn-dn bonding between phosphorus and carbon39. This argument was used to identify structures when or 31PNMR spectra failed96. 

Bicycloannelation.3 The 2 -enolatC (1) of isophoronc reacts with phenyl vinyl sulfone in THF containing 4 equivalents of HMPT (essential) to give the bicycloannelation product 2 in 38% yield. The yield is considerably greater than that obtained from the same reaction using vinyltriphenylphosphonium bromide. Reaction of 1 with isopropenyl phenyl sulfone gives 3 in 21% yield. 

Dienes.1 Cuprates react with vinyltriphenylphosphonium bromide (1) to form phosphoranes, which react with aldehydes to form alkenes. Addition of HMPT to the cuprate favors formation of (Z)-alkenes. 

ALLYI.AMINES Vinyldiphenylphosphine oxide. Vinyltriphenylphosphonium bromide. 

N-Alkyl-P-aminoethylphosphonium bromides, RHN(CH,CH2)P(QH,)3Br (1). These somewhat unstable salts can be obtained in high yield by reaction of primary amines and vinyltriphenylphosphonium bromide in CH,CN. 

In other related syntheses, pyridazines were formed from l,2-diphenyl-3-(diacylmethylene)cyclopropenes, as shown in Eq. (I)46 or from trans-l,2-dibenzoyl-3,3-diphenylcyclopropane 47 Similarly, pyridazines are formed from hydrazines or semicarbazide and y-trichloromethyl-a,jS-unsaturated ketones.48-52 Pyridazines may also be obtained from 1,2-diketones. The reaction between benzoin and hydrazine was investigated in detail. A complex mixture of various compounds is formed, among them 3,4,5,6-tetraphenylpyridazine in low yield.53 Benzil monohydrazones and analogs when treated with vinyltriphenylphosphonium bromide also give 2,3-dihydropyridazines in moderate yield.54,55 Benzil monohydrazone and related compounds react with dimethyl acetylenedicarboxylate to give a mixture of the corresponding ketazine, bisketazine, and pyridazine 2.56 The last is the main product in the absence of solvent. 

The butadienylphosphonium salts (120) are formed in the reactions of phosphines with alkenoyl bromides. Diels-Alder cycloaddition reactions of vinyltriphenylphosphonium bromide with cyclopentadiene and anthracene derivatives have been used (together with conventional quaternization procedures)... 

There are two examples of these syntheses, collected in CHEC-I <84CHEc-I(6)973), one by reaction of an imidazolium JV-ylide with ethyl propiolate <68JA3830>, and another by reaction of imidazole-2-carbaldehyde with vinyltriphenylphosphonium bromide in presence of NaH in THE <76JHClii>. In the early 1990s, the intramolecular 1,5-dipolar cycloaddition reaction of the imidazolium N-allylides (48) to give the pyrrolo[l, 2-a]imidazole (49) has been described. Compound (48) is generated... 

The most general procedure to obtain heteropentalenic mesomeric betaines is the basic treatment of 7V-methyl-5.ff-pyrrolo[l,2-c]imidazole iodide (101). The dipolar intermediate has been trapped with DMAD <89JCS(P1)957>. Iodide (101) is obtained by methylation of 5//-pyrrolo[l,2-c]imidazole (100), easily obtained by reaction of imidazole-4-carbaIdehyde with vinyltriphenylphosphonium bromide in the presence of NaH in THF (Scheme 21) <76tHClli>. 

Vinylmercuric chlorides, 9, 53, 114 a-Vinylnitriles, 20 Vinylsilanes, 13, 82, 279 Vinyltriphenylphosphonium bromide,... 

Methoxy-2-hydroxybenzaldehyde added to a stirred mixture of NaH-dispersion in mineral oil and ether, vinyltriphenylphosphonium bromide and acetonitrile added after the gas evolution has abated, and refluxed 5 days 8-methoxy-2H-1-benzopyran. Y 57.5%. E. E. Schweizer, J. Liehr, and D. J. Monaco, J. Org. Chem. 33, 2416 (1968). 

Another novel dienophile, 2-methylthiomaleic anhydride (88), has provided a new annelative approach to cyclic jS-keto-esters and a-methylene-ketones (Scheme 19), while vinyltriphenylphosphonium bromide (89) has proved useful as both an allene and a keten equivalent (Scheme 20). ... 

Vinyltriphenylphosphonium bromide (VTB) (192) has been used by Posner in an efficient one-pot, three-component [2+2+2] annulation... 

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