99946-23-3Relevant articles and documents
1,3-Diarylcyclopropenes: Syntheses and a Facile Ene Dimerisation
Komatsu, Koichi,Niwa, Tadashi,Akari, Hideaki,Okamoto, Kunio
, p. 2847 - 2881 (2007/10/02)
1,3-Diphenylcyclopropene (3) and its p,p'-dichloro- (4a) and p,p'-dimethyl-derivatives (4b), together with the 3-deuteriated derivative (1,3-diphenylcyclopropene) (3-d), have been prepared by dehydro- or dedeuterio-bromination of the corresponding bromocyclopropanes (6), (16a), (16b), and (6-d2) with ButOK in THF at -30 deg C, whereas the p,p'-dimethoxy-derivative (4c) has been prepared in THF at -78 deg C by protonation of 1-lithio-2,3-bis(p-methoxyphenyl)cyclopropene (18), generated from 1-bromo-2,3-bis(p-methoxyphenyl)cyclopropene (17).All the cyclopropenes (3), (3-d), and (4a-c) are stable only in solution at -78 deg C, and are characterised by means of 13C n.m.r. at this temperature.At higher temperatures, the cyclopropenes (3), (3-d), and (4a-c) readily dimerise to afford the cyclopropylcyclopropenes (7), (7-d2), and (19a-c) in quantitative yields, according to an ene reaction pathway.The cyclopropene (3) also undergoes an ene reaction with tetracyanoethylene, dibenzoylacetylene, and dimethyl acetylenedicarboxylate to give the adducts (13), (14a), and (14b) in moderate yields.Kinetic measurements have been carried out for the ene dimerisation of (3) (at -58 deg, -50 deg, -40 deg, and -30 deg C), (3-d) (at -40 deg and -30 deg C), and (4b,c) (at -30 deg C) in THF.The highly negative ΔS(excit.) value (-137 J mol-1K-1 at 25 deg C) and the fairly large kH/kD value (3.1 at -40 deg and -30 deg C) obtained for the dimerisation of (3) support a concerted mechanism for this reaction.The dimerisation rate of (3) at -30 deg C decreases with substitution by electron-donating groups in the following order: (3) (k2=19.0E-4mol-1s-1), (4b) (10.9E-4), and (4c) (8.3E-4).
