Base-mediated selective synthesis of diversely substituted N-heterocyclic enamines and enaminones by the hydroamination of alkynes.
Regio- and stereoselective alkynylation of various N-heterocycles 1a-l using potassium and cesium salts in DMSO is described. Terminal alkynes 2a-k and internal alkynes 4a-f provided the kinetically stable Z-enamines 3a-l and 5a-i in good to excellent yields using KOH at 120 °C. Addition of heterocyclic amines to 1,3- and 1,4-diethynylbenzene 6a-b provided the mixture of E/Z isomers with KOH; however, with Cs(2)CO(3) selectively Z-isomers 7ab-db were obtained by the hydroamination at one triple bond. This developed methodology also provides an easy and novel access for the synthesis of enaminones 10a-c. The detailed work also supports the formation of cis-isomer by preferential addition of o-haloarylalkynes followed by intramolecular C2 arylation in the copper-catalyzed tandem synthesis of indolo and pyrrolo[2,1-a]isoquinolines.
Synthetic Organic Chemistry Research Laboratory, Department of Chemistry, University of Delhi, Delhi 110007, India.
Megha
M
Joshi
Monika
M
Patel
Rakesh
R
Tiwari
Akhilesh K
AK
Verma
D000480:Alkynes / Q000737:chemistry*; D000586:Amination; D006571:Heterocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D006878:Hydroxides / Q000737:chemistry*; D015394:Molecular Structure; D017680:Potassium Compounds / Q000737:chemistry*; D013237:Stereoisomerism
D000480:Alkynes; D006571:Heterocyclic Compounds; D006878:Hydroxides; D017680:Potassium Compounds; C029943:potassium hydroxide