ABSTRACT
A methodology to generate 2-thio- and 2-oxoimidazoles through an addition-cyclization-isomerization reaction of propargylcyanamides with thiol and alcohol nucleophiles is described. In general, the reaction sequence allows for the rapid formation of highly substituted 2-thio- and 2-oxoimidazoles in good to excellent yields.
Subject(s)
Cyanamide/chemistry , Pargyline/chemistry , Sulfhydryl Compounds/chemical synthesis , Alkynes/chemistry , Cyclization , Isomerism , Magnetic Resonance Spectroscopy , Molecular Structure , Structure-Activity Relationship , Sulfhydryl Compounds/chemistryABSTRACT
A valuable pharmacophore, the 2-aminoimidazole moiety, can be accessed with a variety of substitution patterns through an addition-hydroamination-isomerization sequence (see scheme; R(1),R(4),R(5)=alkyl; R(3)=alkyl, aryl; R(2)=H, alkyl, aryl). The synthesis of the propargyl cyanamide precursors through a three-component coupling enables the preparation of this important heterocyclic core structure in just three steps.
Subject(s)
Biological Products/chemistry , Biological Products/chemical synthesis , Cyanamide/chemistry , Imidazoles/chemical synthesis , Amination , Imidazoles/chemistryABSTRACT
Studies leading to a total synthesis of epothilones B and D are described. The overall synthetic plan was based on late-stage fragment assembly of two segments representing C(1)-C(9) and C(10)-C(21) of the structure. The C(1)-C(9) fragment was prepared by elaboration of commercially available (2R)-3-hydroxy-2-methylpropanoate at both ends of the three-carbon unit. Introduction of carbons 1-4 containing the gem-dimethyl unit was achieved in a convergent manner using a diastereoselective addition of a stannane equivalent of a beta-keto ester dianion. An enantioselective addition of such a stannane equivalent for a beta-keto ester dianion was also used to fashion one version of the C(10)-C(21) subunit; however, the fragment assembly (using bimolecular esterification followed by ring-closing metathesis) with this subunit failed. Therefore, fragment assembly was achieved using a Wittig reaction; this was followed by macrolactonization to close the macrocycle. The C(10)-C(21) subunit needed for this approach was prepared in an efficient manner using the Corey-Kim reaction as a key element. Other key reactions in the synthesis include a stereoselective SmI(2) reduction of a beta-hydroxy ketone and a critical opening of a valerolactone with aniline which required extensive investigation.
