Lead acetate, alcohol oxidations, pyridine

Ceric ammonium nitrate in water or in 50% acetic acid oxidizes ben-zylic alcohols at 90 °C in very good yields [420]. Only catalytic amounts of the reagent and sodium bromate as a reoxidant are needed to convert benzyl alcohol into benzaldehyde in 90% yield on heating in acetonitrile at 80 °C [421]. A similar result is obtained on treatment of benzyl alcohol with lead tetraacetate in pyridine at room temperature for a few hours (yield 85%) [442]. 

Axenrod and co-workers reported a synthesis of TNAZ (18) starting from 3-amino-l,2-propanediol (28). Treatment of (28) with two equivalents of p-toluenesulfonyl chloride in the presence of pyridine yields the ditosylate (29), which on further protection as a TBS derivative, followed by treatment with lithium hydride in THF, induces ring closure to the azetidine (31) in excellent yield. Removal of the TBS protecting group from (31) with acetic acid at elevated temperature is followed by oxidation of the alcohol (32) to the ketone (33). Treatment of the ketone (33) with hydroxylamine hydrochloride in aqueous sodium acetate yields the oxime (34). The synthesis of TNAZ (18) is completed on treatment of the oxime (34) with pure nitric acid in methylene chloride, a reaction leading to oxidation-nitration of the oxime group to em-dinitro functionality and nitrolysis of the A-tosyl bond. This synthesis provides TNAZ in yields of 17-21 % over the seven steps. 

In general reaction of an alcohol with the appropriate anhydride or acid chloride in pyridine at 0-20 JC is sufficient. In the case of tertiary alcohols, acylation is very slow in which case a catalytic amount of 4-dimethylaminopyridine (DMAP) can be added to speed up the reaction by a factor of 10,000. Reaction of polyols with acyl chlorides (1.2 equiv) in the presence of hindered bases (2.0equiv) such as 2,4,6-collidine, diisopropylethylamine or 1,2,2,6,6-penta-methylpiperidine in dichloromethane at -78 °C leads to selective acylation of a primary alcohol. Primary alcohols can also be acylated selectively with isopro-penyl acetate or acetic anhydride in the presence of a catalytic amount of 1,3-dichlorotetrabutyldistannoxane 325.1 [Scheme 4.325].602 The catalyst 325.1 is available commercially or can be easily prepared by simply mixing dibutyltin oxide and dibutyldichlorostannane. No aqueous workup is necessary since the catalyst can be removed by simple chromatography. 

OXICLORURO de FOSFORO (10025-87-3) Fumes in moist air. Contact with water, steam, or alcohols produces hydrochloric acid, phosphoric acid, and phosphine gas, which is pyrophoric, with possible ignition or explosion (may be a delayed reaction). Contact with air produces corrosive fumes. Violent reaction with carbon disulfide, 2,6-dimethylpyiidine-M-oxide, dimethyl sulfoxide, ferrocene-l,l -dicarboxylie acid, pyridine, zinc powder. Reacts, possibly -violently, with acids, alkali metals, alkalis, combustible materials, dimethyl formamide, organic matter, zinc powder. Incompatible with acetic anhydride, iV,A -dimethyl formamide, 2,5-dimethylpyrrole, sodium. Rapid corrosion of steel and most metals, except lead, occurs in the presence of moisture. 

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