Carbamates from nitroso compounds

A fourth type of product, a carbamate RNHCOOR , can be obtained from primary or secondary amines, if these are treated with CO, O2, and an alcohol R OH in the presence of a catalyst. " Primary amines react with dimethyl carbonate in supercritical CO2 (see p. 414) to give a carbamate. " Carbamates can also be obtained from nitroso compounds, by treatment with CO, R OH, Pd(OAc)2, and Cu(OAc)2, " and from nitro compounds. " When allylic amines (R2C=CHRCHRNR 2) are treated with CO and a palladium-phosphine catalyst, the CO inserts to produce the p,y-unsa-turated amides (R2C=CHRCHRCONR 2) in good yields. " Ring-expanded lactams are obtained from cyclic amines via a similar reaction (see also, 16-22). Silyloxy carbamates (RNHC02SiR 3) can be prepared by the reaction of a primary amine with carbon dioxide and triethylamine, followed by reaction with triisopropylsilyl triflate and tetrabutylammonium fluoride. ... 

Carbamates can be obtained from primary or secondary amines by treating these with CO, O2, and an alcohol in the presence of a catalyst [592, 593]. Carbamates can also be obtained from nitroso compounds by treatment with CO, ROH, Pd(OAc)2, and Cu(OAc)2 [594] and from nitro compounds [595, 596]. 

The N-alkylcarbamates and thiocarbam-ates can react with nitrite under mildly acid conditions to form N-nitroso compounds. Nitrite is found in sods, in human saliva, and in cured meats. N-nitrosodimethylamine is formed by soil microorganisms from thiram. Other N-nitroso compounds could similarly be formed from other carbamate pesticides. However, the extent of the reaction of carbamates and nitrite in humans is not known. The N-nitrosodialkylamines formed from dialkylthiocarbamate pesticides and... 

Preparation of 7V-Labeled iV-Nitroso Compounds. The precursor urea, l,3-bis(2-chloroethyl) urea (la, BCU), was prepared in 40% yield by the method of Bestian (9). Its carbamate analog, N-chloroethyl-l-chloroethyl carbamate (2a), was prepared by the method of McQuinn et al. (10). Carbaryl (3a) was purchased from Aldrich Chemical Company (Milwaukee, WI) and was recrystallized from ethanol. 

This chapter is divided into seven main sections. The first of these sections is focused on technological contaminants, namely heterocyclic amines, acrylamide, furan, chloropropanok and their fatty acid esters, polycycKc aromatic hydrocarbons, monocyclic aromatic hydrocarbons, nitroso compounds, and ethyl carbamate. Other sections deal with microbial toxins (mycotoxins and bacterial toxins), persistent organohalogen contaminants (such as polychlorinated biphenyls, dibenzodioxins and dibenzofurans), chlorinated ahphatic hydrocarbons, pesticides (persistent chlorinated hydrocarbons and modem pesticides), veterinary medicines and contaminants from packaging materials. Presented for each of these contaminants are structures, properties, occurrence and the main sources of dietary intake, mechanisms of formation, possibilities of food contamination, prevention and mitigation and health and toxicological evaluations. 

Although food and tobacco products are important sources of external exposure to N-nitrosamines, exposure also occurs from nitrosamines produced internally in the digestive tract. About 5% of ingested nitrates are reduced to nitrites in sahva. These nitrites can subsequently react with secondary and tertiary amines, as well as N-substituted amides, carbamates and other related compounds, to form N-nitroso compounds within the gastrointestinal tract. This internal formation is a major source of human exposure to N-nitrosamines. 

Vol. 28, p. 226, ref. 44 for related work). Similar cycloadditions of dienyl pyrrolidinones [le. AT-(peiita-l,3-dienyl)- or -(buta-l,3-dienyl)-pyrolidin-2-one] with the in situ generated acyl nitroso compound derived from benzyl-JV-hydroxy-carbamate with periodate have led to the preparations of racemic pyroUidines 56 and 57 (R = H or Me). The latter compound is thought to exist as a dimer. An asymmetric synthesis of l,S,6-trideoxy-l,5-imino-D-altritol in which the piperidine ring is formed from a pyiidinium ring bearing Seebach s oxazolidinone chiral auxiliary has also been described. ... 

Since the structures of BCNU and its carbamate analog are identical except for the O-for-NH substitution, this position is clearly the key to the extreme biological reactivity of the latter compound. This point is reinforced by the quite similar in vivo elimination rates of the nitroso-nitrogen of BCNC and nitrosocarbaryl despite the differences in their end groups. The observed reactivity of these compoimds may result from the hydrolytic action of esterases, which are known to attack the C—O bond in carbamate insecticides (38). 

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