1,1′-Carbonyldiimidazole (CDI)

Abstract

(A) 1,1′-Carbonyldiimidazole (CDI) has been efficiently employed in asymmetric synthesis of tetramic acid derivatives 6. In this reaction, CDI transfers a carbonyl group to α-diimines 4 in the presence Of BF 3·OEt2 to afford N-alkyl-4-alkylamino-5-methylene- pyrrol-2-ones 5 in moderate yields. The total asymmetric synthesis of tetramic acid derivatives 6 involves four steps in which the key step is a carbonyl transfer from CDI to the α-ketodiimine.1 (Chemical Equation Presented) (B) Amidation reactions between different sterically hindered acid aldehydes and amines have been reported to be efficiently catalyzed by CDI. First, compound 7 is activated with CDI, then, addition of N,N- diethylethylenediamine (8) to the reaction mixture leads to the imine amide product 9. Remarkable rate enhancement was observed in the reaction due to catalysis by the released carbon dioxide.5 (Chemical Equation Presented) (C) The aqueous CDI-based synthetic method offers an easy and inexpensive way to prepare peptides and peptide thioesters. The synthesis involves reaction of amino acid 10 with CDI to give the amino acid carboxyanhydride intermediate 11 that condenses to both dipeptide 12 and dipeptide thioester 13 in the presence of added amino acid or thiol. Repeated aminoacylation steps on these dipeptide derivatives produce peptide and peptide thioester chains.6-8 (Chemical Equation Presented) (D) Cyanohydrins 14 on stepwise reaction with CDI and O-substituted hydroxylamines 15 give O-substituted 3-hydroxy-4-iminooxazolidin-2-ones 16 in a high-yielding one-pot synthesis.2 Then, sodium methoxide mediated conversion of 16 produces the corresponding O-substituted α-hydroxyamidoximes 17. (Chemical Equation Presented) (E) Recently, the first amidation reaction of unprotected α-amino acids in water under neutral conditions with various aliphatic, aromatic, and heteroaromatic primary amines in the presence of CDI at ambient temperature was reported.4 Zwitterionic amino acids 18 first react with CDI leading to the formation of the intermediate mixed anhydride, followed by nucleophilic attack of amines 19 facilitating the formation of amides 20 in moderate yields. (Chemical Equation Presented) (F) In one of the steps in an enantiospecific pathway described by Davidson and Corey to synthesize an antitubercular tetracyclic oxazole marine natural product called pseudopteroxazole 21, cyclization of the phenol derivative 22 with CDI gave the cyclic carbamate 23 in 94% yield.3 (Chemical Equation Presented) (G) Cyclization of various γ-amino alcohols 24 to substituted azetidines 25 and other N-heterocycles has been conveniently carried out in quantitative yields by using 1,1′-carbonyldiimidazole.9 CDI efficiently activates the hydroxyl groups avoiding the use of toxic reagents and tolerating a wide variety of functional groups. (Chemical Equation Presented). © Georg Thieme Verlag Stuttgart.