Sulphamate esters synthesis

Relatively few high yielding and convenient procedures are available for the synthesis of sulphamic esters, but the reaction of alcohols with sulphamoyl chlorides under basic conditions in the presence of a phase-transfer catalyst provides a simple route [32]. When the ratio of alcohol to sulphamoyl chloride is increased to 2 l, the A-alkyl sulphamic ester is produced (Scheme 3.11). 

The synthesis of esters of sulphamic acids is generally achieved by the reaction of the corresponding sulphamoyl halides with an alkoxide or alcohol according to equation 20. A large variety of such esters have been prepared and the synthetic procedures and their properties have been reviewed1. The present work describes the synthetic procedures which have been developed since 1980 to incorporate the sulphamoyl ester moiety (NS03R) into molecules and to look at the general reactivity of sulphamate esters. 

The study of the electrophilic addition of activated electrophiles across the alkene functional group by Zefirov and coworkers237 has led to the synthesis of a wide range of sulphamate esters. The general approach involves the insertion of S03 into a weak electrophile which generates an activated electrophile that adds readily across carbon-carbon double bonds of olefins (equation 65). 

When sulphur trioxide is added to dialkylchloramines R1R2NC1 (220), where R1 = R2 = Et (220a), R1, R2 = (CH2)5 (220b), R1, R2 = 0(CH2CH2)2 (220c), at - 70 °C followed by olefin addition and then allowing the temperature to rise to ambient the process results in the formation of the / -chloroalkyl sulphamate esters 221 (equation 66). The addition across the double bond occurs in accordance with the Markovnikov rule and leads to the trans configuration. This is shown for cyclohexene in equation 67 and the trans structure is confirmed by independent synthesis by reaction of truns-cyclohexanol with... 

The phase transfer catalysis process has also been extended to synthesize the alkyl and aryl esters (170) of N-aryl sulphamic acids212 (equation 23). If the ratio of aliphatic alcohol (169) to sulphamoyl chloride (168) is increased from 1 1 to 2 1, then N-alkyl-iV-arylsulphamate esters (171) with similar alkyl groups are obtained together with considerable amounts of iV-arylsulphamic acid esters (170). The exclusive formation of the iV-alkyl-iV-arylsulphamate esters (171) can be achieved by employing longer reaction times. A second approach to the synthesis of 171 would be to react the iV-methyl-iV-phenyl sulphamoyl chloride (172) with the alcohol. This was attempted, but the ester failed to form even under forcing conditions. The corresponding AT-alkyl iV-arylsulphamate ion (173) was isolated (equation 24) hydrolysis to the acid was considered to occur as opposed to nucleophilic displacement of the chloride by the methanol. 

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