title: Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enynes and alkynes: computational study of mechanism, reactivity, and regioselectivity.
abstract: The mechanism of Rh-catalyzed (5+2) cycloadditions of 3-acyloxy-1,4-enyne (ACE) and alkynes is investigated using density functional theory calculations. The catalytic cycle involves 1,2-acyloxy migration, alkyne insertion, and reductive elimination to form the cycloheptatriene product. In contrast to the (5+2) cycloadditions with vinylcyclopropanes (VCPs), in which alkyne inserts into a rhodium-allyl bond, alkyne insertion into a Rh-C(sp(2)) bond is preferred. The 1,2-acyloxy migration is found to be the rate-determining step of the catalytic cycle. The electron-rich p-dimethylaminobenzoate substrate promotes 1,2-acyloxy migration and significantly increases the reactivity. In the regioselectivity-determining alkyne insertion step, the alkyne substituent prefers to be distal to the forming C-C bond and thus distal to the OAc group in the product.
authors.affiliation: Department of Chemistry, Nankai University, Tianjin, 300071, PR China. xxfang@nankai.edu.cn
authors.forename: Xiufang
authors.initials: X
authors.lastname: Xu
authors.forename: Peng
authors.initials: P
authors.lastname: Liu
authors.forename: Xing-zhong
authors.initials: XZ
authors.lastname: Shu
authors.forename: Weiping
authors.initials: W
authors.lastname: Tang
authors.forename: K N
authors.initials: KN
authors.lastname: Houk
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D011789:Quantum Theory; D012238:Rhodium / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000480:Alkynes; D009942:Organometallic Compounds; D012238:Rhodium