Titanium chloride-triethylamine

Treatment of N-benzoyl-L-alanine with oxalyl chloride, followed by methanolic triethylamine, yields methyl 4-methyl-2-phenyloxazole-5-carboxylate 32 <95CC2335>. a-Keto imidoyl chlorides, obtained from acyl chlorides and ethyl isocyanoacetate, cyclise to 5-ethoxyoxazoles by the action of triethylamine (e.g.. Scheme 8) <96SC1149>. The azetidinone 33 is converted into the oxazole 34 when heated with sodium azide and titanium chloride in acetonitrile <95JHC1409>. Another unusual reaction is the cyclisation of compound 35 to the oxazole 36 on sequential treatment with trifluoroacetic anhydride and methanol <95JFC(75)221>. 

Tliietane 1-oxide, 380 Thioacetalization, 165-166 Thioanisole-Chlorine. 159 a-Thiobutyrolactone, 158 7-Thiobutyrolactone, 206 Thiochromane-3-carboxylic acids, 385 Thio-Claisen rearrangement, 385 Thiocyanates, 155 Thioethers, 364 Thioglycolic acid, 366 4(5)-Thioimidazoles, 377 Thiol esters, 100 Thiomethoxymethyllithium, 379 Thiones, 175,176 Thionyl chloride, 366 Thionyl chloride-Triethylamine, 367 Thiophenol, 330, 367-368 Thiourea, 278 Titanium(O), 368-369 Titanium (III) chloride, 369 Titanium(III) chloride-Lithium aluminum hydride, 369-370 Titanium (IV) chloride, 228, 370-372... 

N,N,N, N -Tetramethyl-1,3-butanediamine Titanium acetylacetonate Triethylamine Zinc acetylacetonate catalyst, esterification Acetyl acetone Acetyl chloride Ammonium lactate Calcium acetate Cobalt diacetate Cumene sulfonic acid Ethylacetoacetate 2-Ethylhexyl titanate Fluoboric acid Lead acetate... 

Since the introduction of the titanocene chloride dimer 67a to radical chemistry, much attention has been paid to render these reactions catalytic. This field was reviewed especially thoroughly for epoxides as substrates [123, 124, 142-145] so only catalyzed reactions using non-epoxide precursors and a few very recent examples of titanium-catalyzed epoxide-based cyclization reactions, which illustrate the principle, will be discussed here. A very useful feature of these reactions is that their rate constants were determined very recently [146], The reductive catalytic radical generation using 67a is not limited to epoxides. Oxetanes can also act as suitable precursors as demonstrated by pinacol couplings and reductive dimerizations [147]. Moreover, 5 mol% of 67a can serve as a catalyst for the 1,4-reduction of a, p-un saturated carbonyl compounds to ketones using zinc in the presence of triethylamine hydrochloride to regenerate the catalyst [148]. 

Investigations on the trimerization of phenylcyanamide have shown that either triphenylmelamine (12) or triphenylisomelamine (13) is formed, depending on the reaction conditions.1 19,230,231 Under mild conditions (20-80°C) and in the presence of basic catalysts (e.g triethylamine, pyridine) the iso form 13 is obtained, whereas with Lewis acids [e.g., zinc(IT) chloride, titanium(IV) chloride] at 200 °C, triphenylmelamine (12) is formed. 

The synthesis of crystalline, syndiotactic 1,2-polybutadiene is also successful with compounds of titanium, cobalt, vanadium, and chromium [194,206-210]. Alcoholates [e.g., cobalt(II) 2-ethylhexanoate or titanium(III) butanolate] with triethylamine as cocatalyst, are especially well suited for this purpose. They are capable of producing polymers with up to 98% 1,2 structure. Amorphous 1,2-polybutadiene is produced with molybdenum(V) chloride and diethylmethoxyaluminum [211]. Addition of esters of carboxylic acids raises the vinyl content of the products [212]. The influence of the coordination at the center atom is remarkable. Trisallylchromium polymerizes 1,3-butadiene to 1,2-polybutadiene, while bisallylchromchloride gives 1,4-poly butadiene. 

TBDMSCl as Cl Source. TBDMSCl was used as a source of chloride ion in the Lewis acid-assisted opening of an epoxide. The epoxide was treated with TBDMSCl and triethylamine followed by titanium tetraisopropoxide and additional TBDMSCl to give the trans chloride as the major product in 67% yield (eq 10). 

Esterification.—iVAWW -Tetramethylchloroformamidinium chloride, which is readily prepared from iVAWW -tetramethylurea and oxalyl chloride, is an efficient reagent for the esterification of carboxylic acids with alcohols yields of between 66 and 97% are obtained, and the method has also been applied to macrolide synthesis. A modified one-pot procedure for the esterification of carboxylic acids, using phenyl dichlorophosphate-dimethylformamide complex, has appeared. A simple method of activation of carboxylic acids, using methanesulphonyl chloride and triethylamine followed by addition of the alcohol and 4-dimethylaminopyridine, leads to esters in 57— 96% yield for thirteen examples. 0-Methylcaprolactim reacts with carboxylic acids to give methyl esters in 73—91 % yield for seven examples and 2-iodoethyl esters are prepared from acyl chlorides, ethylene oxide, and sodium iodide. Transesterification, catalysed by titanium(iv) alkoxides, provides an effective method for synthesis of esters. Diethyl trichloromethylphosphonate reacts with carboxylic acids to give ethyl esters via transesterification, in 52 to 98 % yield. ... 

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