Oxidation trimerization

It is worth of mentioning that the cross-coupling of 16 and acid derived from hexafluoropropene oxide trimer leads to clean formation of 18 in relatively high yield (Fig. 9.4). More data on the synthesis of five-membered perfluorinated ethers can be found in Chapter 4. 

Burkus [22] was one of the first to report the preparation of isocyanurate-containing urethanes from polyester urethane prepolymers reacted with a triethy-lamine propylene oxide trimerization catalyst. Burkus [15,15a] also reported the preparation of rigid foams by a similar trimerization process. 

Burkus [15a] found that triethylamine and propylene oxide trimerized phenyl-isocyanate to yield the crystalline trimer, m.p. 268°C (uncorr). 

Numerous biocatalytic arene dimerizations mediated by laccases are also described. 3-Hydroxyanthranilic acid 148 is a natural substrate for oxidative dimerization by fungal laccases to give cinnabarinic acid 149, and the applicability of this transformation to other nonnatural substrates has been demonstrated (e.g., 150 to 151) [79, 80]. Crossed dimers arising from the oxidative coupling of two different hydroxyaniline substrates have also been reported [81]. Some more unusual examples of laccase-mediated oligomerizations include the oxidative dimerization/ cyclization of tyrosol 152 to give 153 [82] and the oxidative trimerization of indole 154 to give... 

The hexasubstituted derivatives of triphenylene were among the first discotic meso-gens to be discovered. The most commonly studied derivatives are the hexaethers and hexaesters of 2,3,6,7,10,11-hexahydroxy-triphenylene, and their basic synthesis is illustrated in Scheme 15.1,2-Dimethoxyben-zene (veratrole) is oxidatively trimerized using chloranil in concentrated sulfuric acid to give hexamethoxytriphenylene [40], The reaction takes about a week. Demethyl ation with boron tribromide [41] or hydro-bromic acid [42] yields the hexaphenol. 

Scheme 8.17 PIDA-Induced facile oxidative trimerization to hexahydroxy-triphenylene.

Kumar, S., Manickam, M. Oxidative trimerization of o-dialkoxybenzenes to hexaalkoxyt-riphenylenes molybdenum(v) chloride as a novel reagent. Chem. Commun. 1997,1615-1666... 

Kumar, S., Varshney, S.K. Vanadium oxytrichloride, a novel reagent for the oxidative trimerization of o-dialkoxybenzenes to hexaalkoxytriphenylenes. liq. Cryst. 26, 1841-1843... 

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