Tetraphenyl allene

When colorless crystals of rac-s-trans-3,8-di-tert-butyl-l,5,6,10-tetraphenyl-deca-3,4,6,7-tetraene-l,9-diyne (123) were heated at 140 °C for 2 h, the ben-zodicylobutadiene derivative (126) was produced as green crystals. As shown in the sequence (Scheme 20), 123 is first isomerized to its s-ds-isomer (124), and intramolecular thermal reaction of the two allene moieties through a [2+2] conrotatory cyclization gives the intermediate 125, which upon further thermal reaction between acetylene moieties gives the final product 126 [19,22].This is another example of the crystal-to-crystal reaction. 

Another interesting class of compounds reported by Ando and coworkers is tetrasilacyclohexynes and polysilabridged allenes. Thus, 1,1,2,2,3,3,4,4-octaalkyl-l,2,3,4-tetrasilacyclohexynes (10a and 10b) were prepared and their 29Si NMR spectral data were reported (10a S = -30.8, -19.2 10b -17.7, -8.3)26. 29Si NMR spectral data (—32.2, —7.9) were also reported for l,3,5,5-tetraphenyl-4,4,6,6-tetramethyM,5,6-trisilacyclohexa-1,2-diene (ll)27. 

The synthesis of a tetraphenyl derivative (rubrene, Expt 6.13) of the linearly fused tetracyclic aromatic hydrocarbon naphthacene involves an interesting intermolecular cyclisation process between two molecules of 1-chloro-1,3,3-triphenylpropa-1,2-diene. This substituted allene is formed in situ from 1,1,3-triphenylprop-2-yn-l-ol (Expt 5.41) when the latter is allowed to react with thionyl chloride and the resulting chlorosulphite ester heated with a little quinoline cyclisation occurs spontaneously under these reaction conditions to give rubrene which has an intense red colour. 

The peak at highest mass occurs at m/e 636, and together with fragments corresponding to loss of six CO groups indicates the presence of tetraphenyl-butatrienediiron hexacarbonyl. Allene reacts with Fe2(CO)9 to give the allylic complex (CXV). 

Thermolysis of allene 329 with diphenyldiazomethane in benzene afforded 3-benzylthio-l,3,4,4-tetraphenyl-l-butyne 330 and 2,2,3,3-tetraphenylthiirane 331 in 11% and 87% yields, respectively. Thermolysis of bicyclic allene 332 with diphenyldiazomethane under the same conditions as above gave a mixture of thiirane 331, compound 332, 1,3-dithiolane 334, and tricyclic 335 in 12%, 17%, 13%, and 48% yields, respectively (Equations 49 and 50). It was found that heating of a benzene solution of 335 with diphenyldiazomethane gave a mixture of 333 and 334 together with thiirane 331 in 41%, 29%, and 20% yields, respectively <2000JOC1721>. 

Under similar conditions tetraphenyl allene reacted to give 1,1,3-tri-phenylindene in a yield of 41 % o. th. In this reaction carbon monoxide did not take part (1). However, also in this example cyclic carbonyl compounds were formed in low yield. 2-Diphenyl methyl-3-phenylindone (2) was obtained in 23 % yield besides 17 % of a product which was assumed to be 2,2,4-triphenyl naphthalinone (3). 

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