Tritylamines alkylation

Aliphatic primary and secondary amines can be linked to insoluble supports as ben-zylamines by reductive alkylation with support-bound benzaldehydes or by N-alkyla-tion with support-bound benzyl halides or sulfonates (Figure 3.25 see also Section 10.1). Benzhydrylamines and tritylamines are usually prepared by N-alkylation with the corresponding halides. 

Sterically demanding amines have a high tendency to induce -elimination when treated with alkyl halides. Their alkylation is, however, feasible with reactive alkylating agents, and even 2,2,6,6-tetramethylpiperidines have been N-alkylated (Scheme 6.5). Secondary tritylamines, however, cannot usually be alkylated or acy-lated intermolecularly (last reaction, Scheme 6.4), but examples of intramolecular alkylations have been reported [27]. 

In Schemes 8.204 and 8,205 above we showed that tritylamines can be generated by reductive amination and N-alkylation of trityiamine. However, N-alkyla-tion of amines by triphenylmethyl chloride (mp 110-112 °C) or triphenylmethyl bromide (mp 152-154 °C) in an aprotic solvent such as chloroform or chloro-form-DMF mixtures together with a base such as triethylamine is the most common method for introduting the trityl group [Scheme 8,212]434 4,4 -Dimethoxy-trityl tetrafluoroborate and 4i4, 4"-trimethoxytrityl tetrafluoroborate are also... 

A simple, steieocontrolled synthesis of monofluoro ketomethylene dipepdde isosteres has been developed. N-Tritylated ketomethylene dipeptide isosteres, prepared from N-tritylated amino acids, are converted to their Z-TMS enol ethers and fluorinated with Selectfluor. There is cooperative stereocontrol between the allylic N-tritylamine group and the alkyl group at C-2. The method is short (6 steps) and diastereoselective (85->9S%) and enantioselective (>95%),... 

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