Diphenylmethyl substituted

Diphenylmethyl, substituted 5-diphenylmethyl, and 5-triphenylmethyl thioethers have often been formed or cleaved by the same conditions, although sometimes in rather different yields. As an effort has been made to avoid repetition in the sections that describe these three protective groups, the reader should glance at all the sections. 

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...

Scheme 2. Si-C bond cleavage of diphenylmethyl-substituted organosilanes.

Our approach for starting material suitable as a silyl dianion synthon (D) was via the bis(diphenylmethyl)-substituted silane 15. It was selectively cleaved to give the silyllithium compound 16, which resulted, after a trapping reaction with chlorotrimethylsilane, in disilane 17 (Scheme 3 yield of 17 80 %). The isolated and purified disilane 17 then was cleaved at the Si-C bond with lithium metal, resulting in the lithiated silane 18. Another trapping reaction with chlorotrimethylsilane gave the trisilane 19 (yield of 19 78 %). 

Furthermore functionalized and chiral diphenylmethyl-substituted compounds, like rac-20, are potential precursors for enantiomerically enriched silyllithium compounds [7, 8]. They can be transformed selectively and in good yields to systems of type rac-21. A trapping reaction with chlorotrimethylsilane resulted in the products rac-22 (yield of rac-22 89 %) and 14 (Scheme 4). 

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). 

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