Toluene second step, 71, final steps

Now the most important Route la will be illustrated by means of the synthesis of BIPHEPHOS (Scheme 2.89) [7]. The required biphenyl phosphorchloridite can be prepared by the reaction of PCI3 with 2,2 -dihydroxybiphenol in the presence of NEtj, as suggested by the Amsterdam group [78]. Alternatively, the reaction can be conducted in a suspension of toluene in the absence of a base, under the condition that HCl is removed under vacuum [79]. The chlorophosphite is used in the second step for the condensation reaction with the substituted biphenol in the presence of pyridine. Final crystallization from acetonitrile produces the desired product. Care should be taken with traces of chlorine or acetonitrile, which affects the longterm stability of the diphosphite [80]. These contaminations can be removed by recrystallization, for example, from o-xylene, n-heptane, or ethyl acetate, or by washing with acetone. 

Esterification.—Another way to improve the sometimes unsatisfactory N,N-dicyclohexylcarbodi-imide esterification method is to add catalytic quantities of toluene-p-sulphonic acid to the reaction mixture (c/. 3, 149). Esters can be obtained very rapidly and generally in high yields by reactions between 2-substituted 1,3-benzoxathiolium salts and alcohols (Scheme 30). One drawback could be the rather acidic conditions employed in the second step. A neat modification of the mixed-anhydride esterification method requires no added acid or base in the final step but uses an intramolecular cyclization as the driving... 

As regards benzene and toluene the first and last steps of the reaction arc particularly dangerous, i.e. the vigorous reaction of the hydrocarbon and the final nitration to introduce the second and third nitro group into benzene and toluene respectively. 

In the second method, the alkoxyamine-ftmctionalized backbone is prepared by a chemical modification of a preformed polymer. Abbasian and Entezami prepared alkoxyamine-functionalized poly(vinyl chloride) (PVC) in a three-step procedure. PVC was first arylated with toluene by Friedel-Crafts acylation followed by a bromination step using N-bromosuccinimide. The bromine atom was finally reacted via nucleophilic substitution by the TEMPO hydro-xylamine anion. PVC-g-PS was finally obtained after TEMPO-mediated polymerization of styrene. A TEMPO-functionalized isotactic poly(l-butene) macroinitiator was synthesized by Jo et al. who used a rhodium-catalyzed activation of the alkane C-H bonds and subsequent transformations of the boronate ester group into an hydroxyl pendant group. This reactive moiety was then used to attach a TEMPO-based alkoxyamine bearing another hydroxy function by an ether linkage. A method to prepare PE-g-PS from a poly(ethylene-co-m,p--methylstyrene) obtained by metallocene-catalyzed polymerization was also reported. The macroalkoxya-mine was synthesized after bromination with N-bromosuccinimide followed by a nucleophilic reaction with the TEMPO hydroxylamine anion. 

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