Bartlett demethylation

H-Phosphinates 54 may also serve as precursors for phosphonamidates 56 (Scheme 18).l63 74 75] In the simplest procedure, a N-protected H-phosphinate 54 (produced, for example, by the Baylis procedure,156 see Section 10.10.1.2) is treated with a mixture of CC14, TEA, and the desired amino component. The H-phosphinates are converted in situ into phosphonochloridates 52, which are then trapped by the amine component. Sampson and Bartlett 761 reported improved yields when the H-phosphinate was first treated with bis-(trimethylsilyl)acetamide (BTMSA) to produce the trivalent species 55. They also noted that the reactions are generally cleaner when phosphinate ethyl esters are used instead of phosphinate methyl esters, presumably because the latter are more prone to nucleophilic demethylation. 

Bartlett et al. 191) reported the use of oxidative demethylation of LTA. When 21-deoxyajmaline-l7-( -acetate (304) was oxidized with LTA (1 equiv) in acetic anhydride, 2-hydroxy-21-deoxyajmaline-17-O-ace-tate (305) was produced. However, LTA oxidation (excess of the oxidant) in benzene of the acetate 304 proceeded via oxidative demethylation to give l-demethyl-A -2I-deoxyajmaIine-17-O-acetate (306), which was also... 

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