Tris-chloromethyl mesitylene

The parent hydrocarbon 4 has been obtained by several routes91-93, with the thermal dehydrochlorination of the readily available 2,4,6-tris(chloromethyl)mesitylene (148, equation 12) being particularly valuable92. The yields of this process (close to 50%) are reproducible, making 4 a readily available, albeit difficult-to-handle, highly reactive starting material for further transformations (see below). 

It was also of interest to generate the related symmetric primary benzylic trication. However, the ionization of the 2,4,6-tris(chloromethyl)mesitylene (112) in excess SbF5/S02ClF at -78°C gave apparently only the dienylic allylic dication Lewis acid-base complex (113). The unionized chloromethyl carbon displayed a relatively deshielded NMR absorption, 35.3, indicative of a weak Lewis acid-base interaction. The terminal methylene carbons of the dienylic system showed a 8 C of 197.7 and the terminal carbons of the allylic system displayed a 8 C of 194.8, quite similar to that of the previously described dienylic allylic dications, 107 and 108. 

The most rigid networks form when the polystyrene chains are crosslinked with tris-(chloromethyl)-mesitylene (CMM) [12], since one molecule of this compound connects in space with not two but three polystyrene chains at one junction point. Contrary to this, four subsequent methylene groups in the CMB molecule should strongly contribute to the conformational mobility of cross-bridges and the network as a whole. 

CMDP = 1,4-bis-chloromethyldiphenyl CMM = tris-(chloromethyl)-mesitylene CMB = 1,4-bis-(p-chloromethylphenyl)-butane DMM = dimethoxymethane (methylal) MCDE = monochlorodi-methyl ether XDC =p-xylylenedichloride. 

Figure 7.6 Dependence of equilibrium swelling in n-hexane on the crosslinking degree of networks prepared by crosslinking linear polystyrene with (1) monochlorodimethyl ether (2) tris-(chloromethyl)-mesitylene and (3) 1,4-bls(p-chloromethylphenyl)butane.

Figure 7.9 Dependence of weight swelling in toluene calculated per gram of starting polystyrene on the crosslinking degree of networks prepared by crosslinking (1-6) linear polystyrene and (7) styrene-1% DVB copolymer with (1) 1,4-bis-chloromethyldiphenyl, (2, 7) monochlorodlmethyl ether, (3) tris- chloromethyl)-mesitylene, (4) p-tgrlylene dichloride (5) l,4-bis(p-chloromethylphenyl)butane and (6) dimethylformal (8) gel-type styrene-DVB copolymers.

XDC =p-xylylene dichloride DMM = dimethoxymethane CMM = tris(chloromethyl)mesitylene ... 

Syntheses of the parent [6]radialene (5) were published by three research groups in 1977/1978 4, 5, 6. Among the various gas-phase flash pyrolysis reactions reported, the triple HCl-elimination from l,3,5-tris(chloromethyl)mesitylene (109) is the most practicable one and yields the radialene in 35 -48% yield (Scheme 4.23) [5] other flash pyrolyses were carried out, typically at 900 °C, with cyclododeca-l,5,9-triyne, benzo[l,2 4,5]dicyclobutene derivatives and benzo[l,2-c 3,4-c 5,6-c"]tris(2,5-dihydrothiophene 1,1-dioxide). The sixfold dehydrobromination of hexa(bromomethyl)benzene (110) with methyl lithium at low temperature has been achieved more recently in this case, 5 has been trapped without isolation by cyclopropanation reactions yielding spiro compounds 111 in very low yield [88]. Radialene 5 is a diSicult-to-handle, extremely air-sensitive compound with properties [5] that resemble those described for the parent radialenes 2 and 3 see Sections 4.2.1 and 4.2.2. 

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