Chloroiminium chloride

A stable chloroiminium chloride (173) has been isolated from the chlorination of the heterocyclic enamine (174) (42). 

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-... 

Summary Bis(trimethylsilyl)mercury cleanly reacts at low temperature with chloroiminium chlorides to form stable metal-free cyclic and acyclic diaminocarbenes as well as aryl-, oxy-, chloro-, hydrogeno- and alkyl-amino carbenes. The aryl-, chloro-and hydrogeno-amino carbenes were formed as transient intermediates that undergo dimeri2ation into the corresponding alkenes, which were isolated in good yields. Alkyl-and oxy-amino carbenes were observed at low temperature by C NMR spectroscopy. 

General reaction of a chloroiminium chloride with bis(trimethylsilyl)mercury. 

To probe our synthetic strategy, we first synthesized Alder s stable bis(diisopropylamino) carbene [14]. Starting from bis(diisopropylamino) chloroiminium chloride, we isolate the desired carbene in quantitative yield. 

A similar reaction with bis(dimediylamino) chloroiminium chloride was performed at temperatures below -20 °C and led to the fonnation of the bis(dimethylamino) carbene with a conversion of about 60%. For the first time, the bis(dimethylamino) carbene was formed without complexation with metal cations, which usually occurs in the deprotonation method. The C chemical shift of the carbene carbon atom was significantly shifted toward low field compared to the complexed version. To our surprise, the carbene was not found to dimerize at higher temperatures, but instead a complex mixture was obtained with no traces of dimer being detectable. This raises the question whether the cations are necessary for the dimerization process, as already discussed in literature [7]. 

In our quest to prepare new aryl amino carbenes, we reacted A-diisopropyl-C-phenyl chloroiminium chloride with bis(trimethylsilyl)mercury in THF. The reaction was monitored by C NMR spectroscopy at -78 °C, but the carbene was not observed. Instead, the dimer was formed as a 90/10 mixture of E and Z isomers. 

When the o-acylaminoacetophenone (4.1) is stirred with the chloroiminium chloride, cyclization proceeds in high yield to a quinoline which is an important intermediate in the synthesis of an antihypertensive agent. 

Scheme 1. Retrosynthetic approach to aminocarbenes from chloroiminium chlorides and caiboxamides.

A similar reaction with bis(dimethylamino) chloroiminium chloride was performed at temperatures below -20 °C and led to the formation of the bis(dimethylamino) carbene with a conversion of about 60%. For the first time, the bis(dimethylamino) carbene was formed without... 

Chloroiminium chlorides general procedure) To 1 mole of the N,N-disubstituted carboxylic amide in 500-1000 ml of toluene is added approximately 1.5-2.0 moles of phosgene at 10-25 C. After stirring for several hours the precipitated chloroiminium chlorides are collected by filtration. The obtained yields range from 85-95 %. 

Reaction of the chlorinated Lewis acids carbonic dichloride, phosphoryl chloride, chloroiminium chloride, and chlorine with hexamethylphosphoric triamide... 

Prochiral a-chloroiminium chlorides react with imines having chiral substituents to give... 

Tetrazoles.—Both 1-phenyltetrazole (708) and 2-phenyl tetrazole are protonated at N-4. " 5-Aryl-4-p-dimethylaminophenyl-tetrazoles are formed by the action of hydrazoic acid on AT-p-dimethylaminophenyl-nitrones ArCH=N(0)-QH4NMe2. Tetrazole-5-aldehyde (709), prepared by the action of hydrazoic acid on the acetal (EtO)2CHCN, exists as the dimer (710) in the solid state it reacts with piperidine to give the betaine (711). The carbodi-imide (712) rearranges to the tetrazole (713) on heating. The formation of the 5-diphenyl-amino-tetrazoles (715) by treatment of the chloroiminium chlorides (714) with... 

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