Diphenylmethyl substituted activity

Another parameter investigated was the usefulness of different substituents other than hydrogen or hydroxyl on the Of-carbon. Table II provides the relative activity of several diphenylmethyl substituted 5-pyrimidines. Clearly, the hydroxyl substituted compound is the most active against bean powdery mildew. 

Table II. Activity of Diphenylmethyl-Substituted 5-Pyrimidines Against Bean Powdery Mildew...

With substituents like 9-methylfluorene and diphenylmethane, Si-C bonds can be activated for a cleavage under mild conditions. In contrast to the 9-methylfluorenyl-substituted silanes 7a and 7b, diphenylmethyl-substituted tetraorganosilanes of types 10a, 10b and roc-20 have proven to be valuable precursors for the synthesis of silyllithium reagents like 11a, 11b and rac-21 (Eq. 5). Therefore they correspond well to the silyl anion synthons B. Furthermore the bis(diphenylmethyl)-substituted silane 15 allows a sequential synthesis of unsymmetrical trisilanes and thus is a valuable silyl dianion synthon D (Eq. 6). 

Stable carbon-centered radicals, in particular, substituted diphenylmethyl and triphenylmethyl radicals, couple reversibly with propagating radicals (Scheme 9.11). With, the carbon-centered radical-mediated polymerization systems described to dale, the propagating radical should be tertiary (e.g. methacrylate ester) to give reasonable rates of activation. 

Diphenylmethylcarbanions. The carbanions based on diphenyl-methane (pZ a = 32) (see Table 1) are useful initiators for vinyl and heterocyclic monomers, especially alkyl methacrylates at low temperatures (46). 1,1-Diphenylalkyllithiums can also efficiently initiate the polymerization of styrene and diene monomers that form less stable carbanions. Diphenylmethyl-lithium can be prepared by the metalation reaction of diphenylmethane with butyllithium or by the addition of butyffithium to 1,1-diphenylethylene, as shown in equation 17. This reaction can also be utihzed to prepare ftinctionalized initiators by reacting butyffithium with a substituted 1,1-diphenylethylene derivative. Addition of lithium salts such as hthium chloride, lithium f-butoxide, or lithium 2-(2-methoxyethoxy)ethoxide with 1,1-diphenylmethylcarbanions and other organolithium initiators has been shown to narrow the molecular weight distribution and to improve the stabffity of active centers for anionic polymerization of both alkyl methacrylates and t-butyl acrylate (47,48). 

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