Highly branched ester / Partial optical resolution by mechanical manipulation / Racemic conglomerate melting point diagram / Enantiomer enthalpy and entropy of fusion / Metastable racemic compounds The highly branched ester rac-1 has been prepared. It exists 1.4 kcal mol -1 ) and the moderate value of the corresponding entropy (∆S f enant = 23 ± 4 cal K -1 mol -1 ), both derived from in the form of a conglomerate (m.p. 90-92 °C) in which the two enantiomers are present in separate crystal lattices, as the melting point diagram, are ascribed to the relative compactness of the highly branched molecule and to its indicated by the melting point diagram. Both enantiomers of 1 have been isolated by crystallization [m.p. 112-114 °C, reduced conformational flexibility, respectively. Ester rac-1 has been serendipitously obtained in the form of a racemic [α] D 22 = +24.4 ± 0.7 (c = 0.45, Et 2 O), -25.4 ± 0.8 (c = 0.44, Et 2 O)]; mechanical manipulation of the conglomerate compound (m.p. 82-84 °C) by crystallization of the racemate.
The racemic compound transforms into the conglomerate at provided samples enriched in one or the other enantiomer and subsequent recrystallization of these partially resolved 70 °C. This transformation may be regarded as a spontaneous optical resolution occurring in the solid crystalline state. samples furnished the isolated enantiomers. The high value of the enthalpy of fusion of enantiomers 1 (∆H f enant = 8.8 ±
Over the past years, we have been interested in the syn-[ ] Part 3: Ref. [6c] with α-bromo ester 3 as depicted in Scheme 1. LDA was