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- Title
Organic Reactions in the Solid State: Reactions of Enclathrated 3,4-Epoxycyclopentanone (=6-Oxobicyclo[3.1.0]hexan-3-one) in Tri- o-thymotide and Absolute Configuration of 4-Hydroxy- and 4-Chlorocyclopent-2-en-1-one.
- Authors
Gerdil, Raymond; Liu, Huiyou; Bernardinelli, Gérald
- Abstract
Several aspects of the heterogeneous actions of aqueous and gaseous HCl on the chemical behavior of 3,4-epoxycyclopentanone (=6-oxabicyclo[3.1.0]hexan-3-one; 1) included in the asymmetric cages of tri- o-thymotide (TOT) clathrates belonging to space groups P3121 are described, showing specific features strikingly at variance with those observed in liquid solutions. In a first step, the substrate underwent an acid-promoted allylic isomerization, as already observed in our previous investigations, to give optically active 4-hydroxycyclopent-2-en-1-one ( 2). In a consecutive step, a displacement of the OH group was accomplished by the Cl− anion to afford the corresponding chloro compound 3. Polymorphism was encountered in the preparation of TOT/ 1 clathrates. Recrystallization of TOT in the pure guest 1 yielded micro-twinned crystals belonging to the P31 space group (host/guest ratio 1 : 1), whereas the expected P3121 lattice grew from a mixture of TOT, 1, and MeOH. The structural determination of TOT/ 1 was carried out by X-ray diffraction ( Fig. 1). Kinetic measurements were achieved that shed light on some striking features of this type of heterogeneous reactions for solid-liquid and solid-gas systems. Several reactions of pure clathrate antipodes (+)-TOT/ 1 with gaseous HCl were carried out under various conditions; concentration and enantiomer-excess(ee) determinations of the products 2 and 3 allowed to establish a larger ee for 3, thus demonstrating the influence of the host-guest diastereomeric association on the progression of the reaction. The correlation of optical activities of the host and products for the global reaction disclosed the sequence (+)-( M)-TOT/ 1→(−)- 2→(−)- 3. A new way for the preparation of 2 was devised. It was further demonstrated that the X-ray structure analysis of the chiral clathrate ( M)-TOT/(+)- 2 ( Fig. 4) associated with chiroptical measurements was an efficient and straightforward method to determine the absolute (+)-( R)-configuration of the guest. The enantioselectivity of the TOT clathrate for 2 was established by two different methods which allowed the appraisal of an accurate revised value of the specific rotation of 2. The enclathration of 3 occurred exclusively in the orthorhombic centrosymmetric host lattice Pbca, thus prohibiting the X-ray structural determination of the guest absolute configuration. The problem of finding a pathway to the intended enantiomer enrichment of 3 was worked out through the action of aqueous HCl on microcrystalline (+)-TOT/(−)-( S)- 2 that gave an optically active mixture of unreacted 2 with 3 as sole product. The pure optically active 3 was isolated by subsequent TLC. The resolution of 3 was achieved by GC over a chiral column and its (unknown) specific rotation measured. The absolute configuration of 3 was established by the measurement of the enantiomer purity of the optically active mixture 3 obtained after the total conversion of (−)-( S)- 2 in the presence of thionyl chloride in Et2O, dioxane, and benzene. It was deduced that the (−)- 3 enantiomer had the ( S)-configuration.
- Publication
Helvetica Chimica Acta, 1999, Vol 82, Issue 3, p418
- ISSN
0018-019X
- Publication type
Article
- DOI
10.1002/(SICI)1522-2675(19990310)82:3<418::AID-HLCA418>3.0.CO;2-D