Abstract
Reductive cyclization of 1,3,5-triphenyl- and 3-(2-meth-oxy-phen-yl)-1,5-di-phenyl-pentane-1,5-diones by zinc in acetic acid medium leads to the formation of 1,2,4-tri-phenyl-cyclo-pentane-1,2-diol [1,2,4-Ph3C5H5-1,2-(OH)2, C23H22O2, (I)] and 4-(2-meth-oxy-phen-yl)-1,2-di-phenyl-cyclo-pentane-1,2-diol [4-(2-MeOC6H4)-1,2-Ph2C5H5-1,2-(OH)2, C24H24O3, (II)]. Their single crystals have been obtained by crystallization from a THF/hexane solvent mixture. Diols (I) and (II) crystallize in ortho-rhom-bic (Pbca) and triclinic (P ) space groups, respectively, at 150 K. Their asymmetric units comprise one [in the case of (I)] and three [in the case of (II)] crystallographically independent mol-ecules of the achiral (1R,2S,4r)-diol isomer. Each hydroxyl group is involved in one intra-molecular and one inter-molecular O-H⋯O hydrogen bond, forming one-dimensional chains. Compounds (I) and (II) have been used successfully as precatalyst activators for the ring-opening polymerization of ∊-caprolactone.
Highlights
Reductive cyclization of 1,3,5-triphenyl- and 3-(2-methoxyphenyl)-1,5-diphenylpentane-1,5-diones by zinc in acetic acid medium leads to the formation of 1,2,4triphenylcyclopentane-1,2-diol [1,2,4-Ph3C5H5-1,2-(OH)2, C23H22O2, (I)] and 4-(2-methoxyphenyl)-1,2-diphenylcyclopentane-1,2-diol [4-(2-MeOC6H4)-1,2Ph2C5H5-1,2-(OH)2, C24H24O3, (II)]
1,2-Diphenyl-4-arylcyclopentane-1,2-diols can be readily synthesized by the reductive cyclization of 1,5-diphenyl-3arylpentane-1,5-diones with zinc in an acetic acid medium (Fig. 1; aryl = Ph, 2-MeOC6H4)
When the ratio [diol]/[Mg(BHT)2] = 1:2, and two chains are growing at one diol, the Pn values are somewhat higher than expected (Pn calcd. = 50), which might be explained by a longer reaction time of the second [Mg(BHT)2(THF)2] molecule with the same initiator molecule with respect to the time of polymer-chain propagation
Summary
1,2,4-Triarylcyclopentane-1,2-diols are useful synthetic precursors for obtaining 1,2,4-triarylcyclopenta-1,3-dienes (Hirsch & Bailey, 1978; Yang et al, 2012; Zhang et al, 2013; Ye et al, 2016, 2017). We have tested the obtained diols (I) and (II) as activators of the Mg(BHT)2(THF) precatalyst for polymerization of "-CL (Fig. 2, Table 1). In the case of the ratio [diol]/[Mg(BHT)2] = 1:1 (entries 1 and 3, Table 1), the polymerization degree (the number of polymerized monomer units, Pn) found by 1H NMR spectroscopy and by size-exclusion chromatography (SEC) are very close to the calculated value = 50), which might be explained by a longer reaction time of the second [Mg(BHT)2(THF)2] molecule with the same initiator molecule with respect to the time of polymer-chain propagation This is supported by larger polydispersity index (Ð) values (compare entries 2 and 4 with entries 1 and 3), pointing to unequal growth of the two chains. Using the diol/Mg(BHT) ratio equal to 1:1, the ROP can be carried out in a more controlled manner
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