Carbamates, 1 -hydroxyalkyl synthesis

A classical procedure for the synthesis of the A-(1-chloroalkyl)amides1 or carbamates68 involves substitution of the hydroxy group in stable A-( 1-hydroxyalkyl)amides (or carbamates) by a halogen function with reagents such as thionyl chloride, phosphorus pentachloride, phosphorus pentabromide, etc. In certain cases merely heating in concentrated hydrochloric or hydrobromic acid suffices1. 

Ekin A, Webster DC. (2006) Synthesis and characterization of novel hydroxyalkyl carbamate and dihydroxyalkyl carbamate terminated poly(dimethylsiloxane) oligomers and their block copolymers with poly(e-caprolactone). Macromolecules 39 8659-8668... 

Another possible synthesis is offered by the reaction of alkoxy- or aryloxysulfonylisocyanate to epichloridrine derivatives. The intermediate carbamate easily cyclises upon heating in acetone <07SC2215>. Alternatively phenyl 2-hydroxyalkyl selenides can react with benzoyl isocyanate and the final carbamate cyclize after oxidation of the selenyl functionality <07SC2693>. 

Various methods are available for the preparation of the foregoing precursors to V-acyliminium ions. The most straightforward synthesis of V-(l-hydroxyalkyl)-amides or -carbamates (2 X = OH) involves the addition of primary or secondary amides (carbamates) to aldehydes or ketones. This reaction is an equilibrium process and usually disfavors the adduct except for two special cases. The first involves very reactive aldehydes like formaldehyde, chloral and glyoxylic acid and its esters (equation 4) compounds (4)-(6) are fairly stable compounds that are frequently used in amidoalkylation reactions. The second special case is the intramolecular variant (ring-chain tautomerism), if it leads to five- or six-membered rings (equations 5 and 6). Thus, for n = 1 or 2, (7) and (8) cyclize to (9) and (10), respectively, although the nature of R has an influence on this process. " ... 

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