Naphthyldiphenylmethyl radical

In order to make clear the manner in which we have simplified the treatment of the various radicals, we give in Table IV a statement of the value and significance of the coefficients occurring in the function ip in the individual cases. It will not be necessary to give a similar table for the functions p since, except in the cases of the a and the /3-naphthyldiphenylmethyl radicals which have been discussed above, no simplifications were necessary for them, and the secular equations were solved rigorously. 

A subtle approach198 to the stepwise removal of one member of a family of protecting groups is illustrated by the reductive cleavage of the (1-naphthyldiphenylmethyl) group from 3 -0-(p-anisyldi-phenylmethyl)-5 -0-(l-naphthyldiphenylmethyl)thymidine on treatment with the anthracene radical-anion in oxolane. 3 -0-(p-Anisyldi-phenylmethyl)thymidine was isolated in 87% yield, and the yield of thymidine was only 3%. It is noteworthy that the relative reactivity of 5 -0-(l-naphthyldiphenylmethyl) and 5 -0-(p-anisyldiphenylmethyl) derivatives of thymidine towards radical anions is the reverse of that towards acid. 

Protection of primary hydroxyl groups. The 5 -hydroxyl groups of nucleosides can be protected as the a-naphthyldiphenylmethyl ether. The group is selectively cleaved reductively in the presence of a p-methoxytrityl protecting group by sodium anthracenide in THE (HMPT). Sodium naphthalenide is less selective. The a-naphthyldiphenylmethyl group is relatively stable toward the benzophenone radical anion, which readily cleaves /3,/3,/3-trichloroethyl groups. 

Likewise [cf. equation (4.39)] replacement of a phenyl group in triphenyl-methyl by a-naphthyl greatly reduces the tendency of the radical to dimerize. Naphthyldiphenylmethyl is monomeric in solution at concentrations where triphenylmethyl exists mainly as the dimer. The numerical values of the dissociation constants are, however, not too significant in view of the steric effects present in these very crowded systems (see p. 144). 

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