Reagents alkyl chloroformates

Other reagents that have been used to effect the dehydration of ureas to carbodiimides are alkyl chloroformates (for thioureas) [46], phosgene [47], phosphorus oxychloride [48], and phosphorus pentachloride [38, 49]. Di-chlorocarbodiimides have been shown to be intermediates when COCl2 or PC15 reacts with ureas (Eq. 13). If R1 and R3 are H, then the intermediate... 

Husek, P. and P. Simek. 2006. Alkyl chloroformates in sample derivatization strategies for GC analysis. Review on a decade use of the reagents as esterifying agents. Cum Pharmaceut. Anal. 2 23-43. 

A 2- or 6-hydroxy-substituted purine can be prepared from the corresponding 4,5-diamino-pyrimidinol by cyclization with an acid, ester, ortho ester, or amide. If the ring closure is performed with reagents such as urea, alkyl chloroformates, urethanes, phosgene, and alkyl isocyanates, the 8-hydroxypurines are formed. Various xanthine and uric acid derivatives have been prepared by the condensation of 5,6-diaminopyrimidine-2,4-diols with formic acid. Purin-2-ol (1) was prepared by this route from 4,5-diaminopyrimidin-2-ol and ethyl orthoformate. ... 

Alkyl pyrazole-l-carboxylates 146, which were readily prepared from an alkyl chloroformate and pyrazole 1, are useful alkoxycarbonylating agents towards Grignard reagents for the synthesis of carboxylic esters 147 or towards... 

Alkyl chloroformates CICO2R (R = Me, Et, Bu) have been recently proposed as convenient alkylating reagents for carboxylic acids ... 

Like for conjugation of proteins, reagents should be used at high concentrations in order to increase the probability of the formation of the appropriate conjugates. Relatively insoluble reagents may be added in 5-25% organic solvent (dioxane for alkyl chloroformates. 

Mixed Anhydride Coupling. This very popiilar method, involving the use of alkyl chloroformates as reagents to make anhydrides v/ith acylamino acids or acylpeptides, has been reinvestigated. Determann, Heuer, Pfaender and Reinartz o have shown that exposinre of the mixed anhydride... 

Oxadiazolinones (12a) and thiones (12b) acylate, for example with acetic anhydride, benzoyl chloride or alkyl chloroformates (74TL3875), at ring nitrogen in position 4. 4-Acetyl derivatives have been described as new acylating reagents (76NKK315). In contrast, acetylation of 2-methylamino-5-phenyl-1,3,4-oxadiazole takes place at the methylamino group... 

Protected amines. Amines can be prepared by Gabriel and Mitsunobu syntheses using the iminodicarbonates (1) as nucleophiles. The reagents are available by acylation of 4-methoxybenzylamine with alkyl chloroformates, followed by introduction of the N-Boc group and removal of the benzyl moiety with CAN. 

The 0-protection of A -protected amino acids 55 was achieved by decarboxylative esterification in solvent-free conditions by Colacino et al. (Scheme 4.13). It was found that the use of planetary ball mill was more effective than vibratory mill [8], Commonly used 0-activation reagents (diaUcyl dicarbonate (B0C2O), carbonate (A, A -disuccinimidyl carbonate, DSC), and alkyl chloroformates (ROCOCl, R=Bn, Et, allyl)) were employed in combination with DMAP as base. Reaction parameters had to be optimized for each individual reagent to achieve acceptable yields (selection of results. Table 4.3). Due to high reactivity of benzyloxy chloroformate (Z-Cl), the two-step cycled milling was executed by addition of Z-Cl in 2equiv. portions, so as to consume the chloroformate and reduce the formation of the undesired byproducts. Acidic workup with 10% aqueous citric acid of ether extracts eliminates DMAP and affords the A-protected amino ester derivatives 56 in good yields. 

Acylating agents that have been employed are carbon dioxide, alkyl chloroformates, alkyl formates, add chlorides, esters, benzonitrile and dimethylformamide the expected acylation products from reaction with the above reagents were formed in each case. However, the N,N-dimethyl-amide derivatives of higher carboxylic acids did not yield acylated product as in the case of dimethylformamide . When R = H (equation 63), it was necessary to employ two equivalents of the lithiodithiane due to product enolate formation. 

The carbonylating property of phosgene can be successfully realized using as substitute reagents lower alkyl chloroformates, such as ethyl chloroformate, which is particularly suitable as a ringimidazoline derivatives 5 [26] see also Chapter 6. 

A iridine traces in aqueous solution can be determined by reaction with 4-(p-nitroben25l)pyridine [1083-48-3] and potassium carbonate [584-08-7]. Quantitative determination is carried out by photometric measurement of the absorption of the blue dye formed (367,368). Alkylating reagents interfere in the determination. A iridine traces in the air can be detected discontinuously by absorption in Folin s reagent (l,2-naphthoquinone-4-sulfonate) [2066-93-5] (369,370) with subsequent chloroform extraction and hplc analysis of the red dye formed (371,372). The detection limit is ca 0.1 ppm. Nitrogen-specific thermal ionisation detectors can be used for continuous monitoring of the ambient air. 

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