title: Direct cyclopropanation of 1-alkynylphosphonates by Cp2ZrCl2/2EtMgBr/2AlCl3 to afford cyclopropylmethylphosphonates.
abstract: [reaction: see text] The reagent system Cp2ZrCl2/2EtMgBr/2AlCl3 converts 1-alkynylphosphonates into cyclopropylmethylphosphonates 3 in good isolated yields. Ethers, chlorides, and other cyclopropyl groups are compatible with the reaction conditions. Deuterium labeling is consistent with the formation of stable cyclopropylmethylbimetallic phosphonates by ring contraction of the corresponding aluminacyclopentenylphosphonate. Temperature is crucial; apparently, the cyclopropylmethylbimetallic phosphonates are in equilibrium with the aluminacyclopentenylphosphonates. Low temperature favors the former. We surmise that the negative charges of the intermediate are stabilized by the phosphonate group. Thus, diphenylacetylene and 3-hexyne failed to give cyclopropyl products under the same reaction conditions.
authors.affiliation: Department of Medicinal Chemistry and Natural Products, School of Pharmacy, Hebrew University in Jerusalem, Jerusalem 99120, Israel.
authors.forename: Abed Al
authors.initials: AA
authors.lastname: Aziz Quntar
authors.forename: Morris
authors.initials: M
authors.lastname: Srebnik
mesh_terms: D000478:Alkylation; D000077410:Aluminum Chloride; D017607:Aluminum Compounds; D001965:Bromides; D002712:Chlorides; D003500:Cyclization; D007202:Indicators and Reagents; D008274:Magnesium; D063065:Organophosphonates / Q000138:chemical synthesis* / Q000737:chemistry*; D015040:Zirconium
chemical_list: D017607:Aluminum Compounds; D001965:Bromides; D002712:Chlorides; D007202:Indicators and Reagents; D063065:Organophosphonates; D000077410:Aluminum Chloride; D015040:Zirconium; D008274:Magnesium; C429984:zirconium chloride