Hydantoins carbodiimides

The reaction with asymmetric carbodiimides are generally highly chemo- and regioselec-tive, affording one single regioisomeric hydantoine." ... 

Intramolecular cyclization also occurs in the reaction of the arylidene hydantoin derived carbodiimides 15, which cyclizes in situ to give imidazo[l,5-c][l,3]benzodiazepines... 

Carbodiimides are known to react with primary amines to form guanidines.f In the case of amino acid esters, a subsequent elimination of alcohol is possible with formation of an imino-hydantoin species (Scheme 8). However, these reactions usually require higher temperatures or the occurrence of acid catalysis and therefore can be neglected when unprotonated amino acid derivatives are acylated using carbodiimides. On the other hand, this side reaction becomes more important when protonated amino acids (i.e., amino acid ester hydrochlorides) are coupledf and these byproducts may occur. 

A hydantoin library of 800 compounds has been reported by Dress-mann et al. [61]. In this approach, 20 different amino acids and over 80 primary amines were incorporated. Selected amino acids were attached via their iV-terminus to hydroxymethyl polystyrene resin by using a carbamate linker. This enabled generation of the free acid resin-bound intermediates, which could then be converted to their corresponding amides by standard carbodiimide coupling reactions and excess primary amine. Concomitant... 

DCBTF 3,4-DCBTF. See 3,4-Dichlorobenzotrifluoride DCC DCCD. See Dicyclohexyl carbodiimide DCCNa. See Sodium dichloroisocyanurate DCD. See Dicyandiamide DCDMH. See 1,3-Dichloro-5,5-dimethyl hydantoin... 

Two alternative pathways have been proposed for the reaction of carbodiimides (127) with activated Q ,j8-unsaturated carboxylic acids (126), based on DFT calculations the reaction, which affords hydantoins (130) and variable amounts of At-acyl ureas (129), may proceed either via imino-oxazolidinones (128) or At-acyl ureas (129), as the overall barriers are similar for both pathways. A second molecule of carboxylic... 

Two alternative pathways featuring IV-acyl ureas and imino-oxazolidinones as intermediates for the formation of the hydantoin from reaction of carbodiimides and activated a,j8-unsaturated carboxylic acids have been studied using computational methods and the overall barriers are similar (Scheme 82)P ... 

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