Chloroiminium salts chloride

Formation of Chloroiminium Salts. Oxalyl chloride reacts... 

For example, efficient syntheses of thioamides and thio-lactams are based on this methodology. Certain types of chloroiminium salts can serve as precursors for high-energy synthetic intermediates. Thus, azomethine ylides were obtained by treatment of -acylamino carboxylic esters with oxalyl chloride (eq 24). ... 

Various iminium salts have been studied as reagents for the alcohol to halide transformation (see also 1,173) " for example the chloroiminium phospho-chloridates (75a) and chlorides (75b), prepared from amides with POCI3 and SOCI2, respectively, and the bromoiminium bromides (75c), made from (75b) by treatment with HBr, have been used to convert alcohols to the chlorides and bromides (Scheme 36). 

Acylation. Acylation is the most rehable means of introducing a 3-substituent on the indole ring. Because 3-acyl substituents can be easily reduced to 3-aLkyl groups, a two-step acylation—reduction sequence is often an attractive alternative to direct 3-aLkylation. Several kinds of conditions have been employed for acylation. Very reactive acyl haUdes, such as oxalyl chloride, can effect substitution directiy without any catalyst. Normal acid chlorides are usually allowed to react with the magnesium (15) or 2inc (16) salts. The Vilsmeier-Haack conditions involving an amide and phosphoms oxychloride, in which a chloroiminium ion is the active electrophile, frequentiy give excellent yields of 3-acylindoles. 

A potentially mote interesting application of the method for asymmetric synthesis - uses chiral a-chloroiminium chlorides as starting material. Best results are obtained with iminium salts derived from (2S)-(methoxymethyl)pyrrolidine. They react with imines in the presence of triethylamine to give opti-... 

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