Acetamides, to protect amines

Because the enamine functionality underwent a facile cyclizadon reacdon when the nitro group was reduced, the first step of this process was conversion of the enamine to the diethyl acetal 33 by treatment with ethanol containing sulfuric acid catalyst at reflux. The nitro group was reduced to an amine without significant concomitant cyclizadon and protected as its acetamide 34. The acetal protecting group was removed under ndld acidic condidons (pyridinium p-toluenesulfonate and... 

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. 

Chlorophenyl)glutarate monoethyl ester 87 was reduced to hydroxy acid and subsequently cyclized to afford lactone 88. This was further submitted to reduction with diisobutylaluminium hydride to provide lactol followed by Homer-Emmons reaction, which resulted in the formation of hydroxy ester product 89 in good yield. The alcohol was protected as silyl ether and the double bond in 89 was reduced with magnesium powder in methanol to provide methyl ester 90. The hydrolysis to the acid and condensation of the acid chloride with Evans s chiral auxiliary provided product 91, which was further converted to titanium enolate on reaction with TiCI. This was submitted to enolate-imine condensation in the presence of amine to afford 92. The silylation of the 92 with N, O-bis(trimethylsilyl) acetamide followed by treatment with tetrabutylammonium fluoride resulted in cyclization to form the azetidin-2-one ring and subsequently hydrolysis provided 93. This product was converted to bromide analog, which on treatment with LDA underwent intramolecular cyclization to afford the cholesterol absorption inhibitor spiro-(3-lactam (+)-SCH 54016 94. 

The C 0 bonds of ethers, acetals, and esters are cleaved with iodotrimethylsilane (eq (39)) [36]. Various halosilanes, silylamines, and N,0-bis(trimethylsilyl)acetamide are used not only for the protection of alcohols, amines, and carboxylic acids but also for the conversion of them to the volatilizable compounds for GC analysis (eq (40)) [37]. Silyltriflates act as silating agents as well as Lewis acids (eq (41)) [38]. 

AC2O. It is cleaved by methanolysis with NaOMe/MeOH to open the ring followed by reductive desulfurization with Bu SnH/AIBN. This leaves the amine protected as an acetamide. ... 

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