Isothiocyanates, addition salts

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

The addition of isocyanides and azide to aldehyde-derived enamines has led to tetrazoles (533,536). On the other hand the vinylogous amide of acetoacetic ester and related compounds reacted with aldehydes, isocyanides and acids to give a-acylaminoamides (534). Iminopyrrolidones and imino-thiopyrrolidones were obtained from the addition of cyclohexylisocyanide and isocyanates or isothiocyanates to enamines (535). An interesting method for the formation of organophosphorus compounds is found in the reactions of imonium salts with dialkylphosphites (536). 

Ammonia and primary and secondary amines can be added to isocyanates to give substituted ureas. Isothiocyanates give thioureas. This is an excellent method for the preparation of ureas and thioureas, and these compounds are often used as derivatives for primary and secondary amines. Isocyanic acid (HNCO) also gives the reaction usually its salts (e.g., NaNCO) are used. Wohler s famous synthesis of urea involved the addition of ammonia to a salt of this acid. "... 

Salts of dithiocarbamic acid can be prepared by the addition of primary or secondary amines to carbon disulfide. This reaction is similar to 16-9. Hydrogen sulfide can be eliminated from the product, directly or indirectly, to give isothiocyanates (RNCS). Isothiocyanates can be obtained directly by the reaction of primary amines and CS2 in pyridine in the presence of DCC. ° In the presence of diphenyl phosphite and pyridine, primary amines add to CO2 and to CS2 to give, respectively, symmetrically substituted ureas and thioureas ... 

Despite the chemical diversity of the several hundred structures representing herbicidal activity, most reactions of herbicides fall within only a limited number of mechanistic types oxidation, reduction, nucleophilic displacements (such as hydrolysis), eliminations, and additions. "Herbicides", after all, are more-or-less ordinary chemicals, and their principal transformations in the environment are fundamentally no different from those in laboratory glassware. Figure 2 illustrates three typical examples which have received their share of classical laboratory study—the alkaline hydrolysis of a carboxylic ester (in this case, an ester of 2,4-dichlorophenoxyacetic acid, IX), the cycloaddition of an alcohol to an olefin (as in the acetylene, VI), and the 3-elimination of a dithiocarbamate which provides the usual synthetic route to an isothiocyanate (conversion of an N.N-dimethylcarbamic acid salt, XI, to methyl isothiocyanate). Allow the starting materials herbicidal action (which they have), give them names such as "2,4-D ester" or "pronamide" or "Vapam", and let soil form the walls of an outdoor reaction kettle the reactions and products remain the same. 

Acrylates can also be used in Michael addition with primary amine and, after further reaction with isothiocyanate, supported thioureas are isolated. These can then undergo a cleavage under basic conditions leading to cyclisation and formation of tetrahydrothioxopyrimidinones [129], Onium salts supported isothiocyanates can also be used with this methodology and lead to the formation of various guanidines [130] (Fig. 41). 

Dithiocarbamic esters can generally be obtained easily by alkylation or arylation of the corresponding dithiocarbamic salts 792-798 other methods are addition of thiols to isothiocyanic esters,792 treatment of chlorodithio-formic esters with amines,792 and reaction of thiocarbamoyl chlorides with thiolates.786... 

With the help of a combination of selective dissolution and chromatographic separation, several of the cyclic ethers have been separated and isolated <2003OL3745>. Though not of synthetic value, gas-phase cyclization reactions of acylium ions with nitriles, forming 1,3,5-oxadiazinium ions 375 by double nitrile addition followed by cyclization, have been reported (Scheme 75) <2001MI445>. Similarly, the gas-phase reactions of acylium and thioacylium ions with isocyanates (18 Y = 0) and isothiocyanates (18 Y = S) have been reported to result in oxadiazinium (16 X = 0) and thiadiazinium (16 X = S) salts, respectively (see Scheme 2) <2005JAM1602>. 

An interesting topological effect is the increased terminal chlorination of fatty acids when they are adsorbed and aligned on alumina Silicon disulfide and particularly boron sulfide have been used with advantage instead of phosphorus pentasulfide to replace carbonyl oxygen by sulfur The addition of sulfur monochloride to olefins followed by reduction of the adduct with sodium sulfide provides a convenient inexpensive route to a large number of episulfides A direct conversion of ar. nitro compounds to isothiocyanates has been reported Sec. phosphines add easily to olefins under UV-irradiation Advances in peptide synthesis include the use of acyloxyphospho-nium salts prepared with hexamethylphosphoramide a simple synthesis with triphenyl phosphite , and the use 4-picolyl esters at the... 

A standard condition has been optimized for this reaction, in which the aryl amine is diazotized in 10 times its amount of acetic acid, followed by the addition of one equivalent of cuprous halide in hydrohalic acid. Under these conditions, the acetate salt of aryl amine is relatively soluble, and less froth and tarry material are formed during diazo transformation. In addition, chlorination, bromination, and iodonation of p-haloaniline to dihalobenzenes under such standard conditions give almost comparable average yields. Other modifications of this reaction include the formation of phenyl selenocyanate by the reaction with potassium selenocyanate, and aryl nitrile by the reaction with nickel cyanide. Moreover, this reaction has been extended to the preparation of phenyl thiocyanate, phenyl isothiocyanate and aromatic sulfonyl chloride. ... 

From aminoguanidines and diaminoguanidines. Aminoguanidine salts react additively with aroyl isothiocyanates in methanol to form linear... 

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