Direct cyclopropanation of 1-alkynylphosphonates by Cp2ZrCl2/2EtMgBr/2AlCl3 to afford cyclopropylmethylphosphonates.
[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.
Aziz Quntar
Abed Al
AA
Department of Medicinal Chemistry and Natural Products, School of Pharmacy, Hebrew University in Jerusalem, Jerusalem 99120, Israel.
Srebnik
Morris
M
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
D017607:Aluminum Compounds; D001965:Bromides; D002712:Chlorides; D007202:Indicators and Reagents; D063065:Organophosphonates; D000077410:Aluminum Chloride; D015040:Zirconium; D008274:Magnesium; C429984:zirconium chloride