Au(I)-catalyzed cascade reaction involving formal double hydroamination of alkynes bearing tethered carboxylic groups: an easy access to fused dihydrobenzimidazoles and tetrahydroquinazolines.
A process involving gold(I)-catalyzed formal double hydroamination of alkynes, bearing a tethered carboxylic group, for the synthesis of fused dihydrobenzimidazoles and tetrahydroquinazolines has been developed. A series of transition metal catalysts have been screened for this transformation, and a catalyst system consisting of Ph(3)PAuCl (1 mol %) and AgOTf (1 mol %) was found to be the best. The procedure entails the reaction of easily accessible starting materials such as alkynoic acids and 1,2-diaminobenzenes/2-aminobenzylamines in the presence of the catalyst in 1,2-dichloroethane at 100 degrees C. In the case of alpha-substituted alkynoic acids, the corresponding products were obtained in high diastereoselectivities; the structure of the diastereomers has been unambiguously characterized by NMR techniques. The mechanism of the reaction is discussed, and the origin of the diastereoselectivities is addressed. It was observed that under the microwave irradiation conditions, the reaction time is significantly shortened (0.5 h).
Patil
Nitin T
NT
Organic Chemistry Division II, Indian Institute of Chemical Technology, Hyderabad 500 607, India. patilnitint@yahoo.com
Mutyala
Anil Kumar
AK
Lakshmi
Pediredla G V V
PG
Gajula
Balakrishna
B
Sridhar
Balasubramanian
B
Pottireddygari
Gurava Reddy
GR
Rao
Tadikamalla Prabhakar
TP
D000480:Alkynes / Q000737:chemistry*; D000586:Amination; D001562:Benzimidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D002264:Carboxylic Acids / Q000737:chemistry*; D002384:Catalysis; D006046:Gold / Q000737:chemistry*; D015394:Molecular Structure; D050607:Organogold Compounds / Q000737:chemistry*; D011799:Quinazolines / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D000480:Alkynes; D001562:Benzimidazoles; D002264:Carboxylic Acids; D050607:Organogold Compounds; D011799:Quinazolines; D006046:Gold