To thioamides

The microwave-assisted thionation of amides has been studied by Ley and coworkers using a polymer-supported thionating reagent [115]. This polymer-supported amino thiophosphate serves as a convenient substitute for its homogeneous analogue in the microwave-induced rapid conversion of amides to thioamides. Under microwave conditions, the reaction is complete within 15 min, as opposed to 30 h by conventional reflux in toluene (Scheme 7.95). The reaction has been studied for a range of secondary and tertiary amides and GC-MS monitoring showed that it proceeded almost quantitatively. More importantly, this work was the first incidence of the use of the ionic liquid l-ethyl-3-methylimidazolium hexafluorophosphate... 

Another example of microwave-assisted PSR chemistry involves the rapid conversion of amides to thioamides by use of a polystyrene-supported Lawesson-type thio-nating reagent. By use of microwave irradiation at 200 °C in sealed vessels (monomode reactor), a range of secondary and tertiary amides was converted within... 

Addition to thioamides.s Alkyl- or aryllithiums add to the carbon-sulfur bond of aromatic thioamides to give adducts that are hydrolyzed to unsymmetrical ketones. Reduction of the adducts with LiAlHj before hydrolysis provides a-alkylated amines. 

The reaction of thioaldehydes, generated from phosphonium ylides and sulphur with secondary amines such as dimethylamine, leads to thioamides. If the thioaldehydes possess a a-hydrogen atom enamines are produced (equation 103)326. 

An alternate step-wise cyclization strategy to form 3-carboline 22 is shown in Scheme 7. Acylation of D-tryptophan (21) with piperonyloyl chloride afforded amide 25, which was converted to thioamide 26 with Lawesson s reagent. Thioamide 26 was treated with methyl iodide in refluxing CH2CI2 to give a a-thiomethylimmonium ion, which was trapped by the intramolecular addition of indole. The thiomethyl group was... 

Hydrolysis of nitriles.1 N itriles are converted to thioamides by reaction with I (2 equivalents) at 40° overnight. Under these conditions most other functional groups are stable. Kinetic studies indicate that the reaction with nitriles is a two-step process, the first of which is analogous to an enc reaction to give a. Thioamides arc particularly useful precursors to amines by the method of Borch (2, 430 431), reaction with triethyloxonium tetrafluoroborate followed by reduction withNaBHj..- ... 

Thermolysis of 4//-l,3-thiazines (271) leads to thioamide vinylogues (272) by ring opening (Scheme 110) (86SC79). At more elevated temperature (toluene reflux), compound 273 is not isolated. A heterocyclic isomer (274) with a 3,4-dihydro-2//-l,3-thiazine structure is obtained (Scheme 111). 

New polymer-supported reagents for sulfide transfer have been developed to avoid exposure to malodorous and toxic sulfur reagents. Ley et al.15 prepared a stable aminothiophosphate polystyrene resin for the conversion of secondary and tertiary amides to thioamides in high conversion and purity (Table III, entry 11). This procedure is extremely clean and affords the desired product with short reaction times in comparison to Law-esson s reagent. In addition, the aminothiophosphate resin dehydrates primary amides to nitriles. 

In contrast, the reaction of thionoesters bearing a /Tcarbonyl group with primary amines does not lead to thioamides, but instead to a-oxo ami-noketene acetals, arising from elimination of H2S rather than ROH [71]. 

Question A.18 Why are p adrenergic blocking agents needed in addition to thioamides at the onset of treatment of hyperthyroidism ... 

A few 6- and 8-cyanopurines have been prepared and undergo characteristic nitrile addition reactions rather readily. Thus, alkaline hydrolysis produces carboxamides, then carboxylic acids, alcoholysis leads to imidates, ammonolysis to amidines, hydrazinolysis to amidhydrazines, hydroxylamine to amidoximes, and hydrogen sulfide to thioamides. Acid hydrolysis tends to give the decarboxylated acid derivative. Reduction either by sodium-ethanol or, preferably, by catalytic hydrogenation affords aminoalkylpurines and addition of Grignard reagents produces, in the first place, acylpurines. As with aldehydes, most of the compounds examined have been relatively non-polar derivatives. Table 28 lists some reactions and relevant literature. 

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