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Mechanistic Study on the Cleavage and Reorganization of C(sp 3 )H and CN Bonds in Carbodiimides: Synthesis of 1,2‐Dihydrothiopyrimidines and 2,3‐Dihydropyrimidinthiones through Four‐Component Coupling
Author(s) -
Wang Yang,
Zhao Fei,
Zhou Yi,
Chi Yue,
Wang Zitao,
Zhang WenXiong,
Xi Zhenfeng
Publication year - 2013
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201301633
Subject(s) - chemistry , cycloaddition , bond cleavage , carbodiimide , cleavage (geology) , ring (chemistry) , isomerization , stereochemistry , ketenimine , catalysis , organic chemistry , fracture (geology) , geotechnical engineering , engineering
This study sheds light on the cleavage and reorganization of C(sp 3 )H and CN bonds of carbodiimides in a three‐component reaction of terminal alkynes, sulfur, and carbodiimides by a combination of methods including 1) isolation and X‐ray analysis of six‐membered‐ring lithium species 2‐ S , 2) trapping of the oxygen‐analogues ( B‐ O and D‐ O ) of both four‐membered‐ring intermediate B‐ S and ring‐opening intermediate D‐ S , 3) deuterium labeling studies, and 4) theoretical studies. These results show that 1) the reaction rate‐determining step is [2+2] cycloaddition, 2) the CN bond cleavage takes place before C(sp 3 )H bond cleavage, 3) the hydrogen attached to C6 in 2‐ S originates from the carbodiimide, and 4) three types of new aza‐heterocycles, such as 1,2‐dihydrothiopyrimidines, N ‐acyl 2,3‐dihydropyrimidinthiones, and 1,2‐dihydropyrimidinamino acids are constructed efficiently based on 2‐ S . All results strongly support the idea that the reaction proceeds through [2+2] cycloaddition/4π electrocyclic ring‐opening/1,5‐H shift/6π electrocyclic ring‐closing as key steps. The research strategy on the synthesis, isolation, and reactivity investigation of important intermediates in metal‐mediated reactions not only helps achieve an in‐depth understanding of reaction mechanisms but also leads to the discovery of new synthetically useful reactions based on the important intermediates.