Triafulvenes with methyl

For decades, it has been well known that triafulvene reacts with various 1,3-dipoles, and the modes of the reaction depend on the nature of the 1,3-dipole as well as the substituents on the triafulvenes. For example, triafulvene 308 treated with pyridium ylide 309 to give pyran derivative 310 was reported by Eicher et al. The same reaction with methyl (triphenylphosphoranylidene)acetate 311 gave the cyclobutene derivative 312 (Scheme 7.68) [79]. Alternatively, treatment oftriaful-vene 308 with isoquinolinium ylide 313 afforded furan derivative 314. The mechanism of these reactions, proposed by the authors, is depicted in Scheme 7.69. 

Ketene acetals show a pattern of product formation very similiar to enamines79 Diphenyl-4,4-diacetyl triafulvene is converted to diacetylmethyl cyclopentadiene 529 by S,N-acetals, whilst diphenyl-4,4-dicyano triafulvene undergoes C—C-inser-tion to S,N- and N,N-acetals, e.g. 530/531, resulting in cross-conjugated systems 533/534 by analogy with enamines. Cyclic S,N-acetals 532, however, yield exclusively the bicyclic fulvenes 535 due to additional loss of methyl mercaptan. 

Decarboxylation of methyl chlorodifluoroacetate with lithium chloride in HMPA in the presence of chlorodifluoroacetophenone yields mainly 1-chloro-l-phenyldifluoroethylene, probably by the mechanism shown in Scheme 11. Pyrolysis of the acid chlorides, CFs O CFs CFa COCl and HCF2 (CF2)6 COCl, causes loss of COFCl and formation of the olefins, CFs O-CFiCFs or HCF2 (CF2)3 CF CF2. Addition of bistrifluoromethylketen to bis-p-tolylcyclo-propenone yields triafulvene (13), which has a dipole moment of 7.42 D, suggestive of considerable charge separation. 

Tetrachlorocyclopropene (22) and a variety of active methylene compounds are building blocks for hexasubstituted [3]radialenes, as was first reported by Fuku-naga et al. Thus, 22 reacted with malononitrile, dimethyl malonate, and methyl cyanoacetate in glyme in the presence of an excess of NaH to give triafulvene dianion salts 23, which were isolated as tetrabutylammonium salts (Scheme 4.4)... 

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