title: Theoretical studies on the mechanism of the C-H amination of silyl cyclopropenes by azodicarboxylates.
abstract: DFT/M06 calculations were carried out to better understand the mechanism and regio- and chemoselectivities of our previously discovered formal C-H amination of silyl cyclopropenes by azodicarboxylates (Chem. Commun. 2012, 48, 10990). The results revealed that the initial Alder-ene reaction between the two reactants follows a stepwise mechanism and the subsequent allylic transposition proceeds via a concerted [1,3]-migration of hydrazodicarboxylate. For the Alder-ene process of 1-silyl-2-methylcyclopropene, different electronic effects of the substituents make the C1 much more negatively charged and thus more reactive than C2 in the regiochemistry-determining electrophilic azodicarboxylate addition step. In addition, the poor regioselectivity caused by a C2 ether linkage and the lower reactivity of ene donors other than cyclopropenes with azodicarboxylate were well explained by the computational results. Furthermore, the divergent allylic transposition of the Alder-ene intermediates was rationalized, and the steric repulsion between the silyl group and the hydrazodicarboxylate moiety was suggested as the driving force in promoting the allylic transposition. The barrier for the rate-controlling [1,3]-migration of hydrazodicarboxylate from an intermediate containing the C1-N bond is 21.1 kcal/mol, whereas a higher barrier of 27.5 kcal/mol is required for the similar rearrangement of the thermodynamically more stable intermediate containing the C2-N bond.
authors.affiliation: College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou, Zhejiang Province 325035, People's Republic of China.
authors.forename: Genping
authors.initials: G
authors.lastname: Huang
authors.forename: Yuanzhi
authors.initials: Y
authors.lastname: Xia
authors.forename: Chunrui
authors.initials: C
authors.lastname: Sun
authors.forename: Jingwei
authors.initials: J
authors.lastname: Li
authors.forename: Daesung
authors.initials: D
authors.lastname: Lee
mesh_terms: D000586:Amination; D001391:Azo Compounds / Q000737:chemistry*; D003521:Cyclopropanes / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008962:Models, Theoretical; D012821:Silanes / Q000737:chemistry*; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D001391:Azo Compounds; D003521:Cyclopropanes; D012821:Silanes