Powdered host compounds, inclusion

Another variation of the enantioselective inclusion complexation procedure leading to optical resolution is the application of powdered host compounds in the... 

A powdered 1 1 inclusion complex of (-)-l and 4-methoxy-l-methylpyridone 2c was irradiated by 100-W high-pressure Hg-lamp at room temperature in the solid state. The crude reaction product was chromatographed on silica gel using CHCI3 as a solvent to give a mixture of host compound and 3, from which 3 was isolated by distillation as an oil ([a]D-123° (c 0.026, CHC13), 100% ee). 

For example, when a suspension of powdered optically active host 3a was mixed with racemic 1-phenylethanol (4a) in a 1 1 molar ratio and stirred at room temperature for 6 h, a 2 1 inclusion complex was formed. When the filtered solid complex was heated in vacuo, it gave (—)-4a (95 % ee, 85 % yield). For the host compounds 3a-c, approximately the same ee (78-99.9 %) and high yield (75-93 %) could be achieved in the resolution of alcohols of the 4 and 5 series in water and hexane. It has been found that introducing... 

When a mixture of powdered ketone and NaBH4 is kept at room temperature, reduction of the ketone occurs to give the corresponding alcohol [2], When the reaction is carried out in inclusion crystals containing a chiral host compound, the optically active alcohol can be obtained by enantio-control of the reaction by the chiral host. For example, treatment of inclusion crystals of acetophenone (2a) or o-methylacetophenone (2b) and (S,S)-(-)-1,6-bis(o-chlorophenyl)-1,6-diphenylhexa-2,4-diyne-l,6-diol (1) [3] with powdered BH3-ethylenediamine complex (3) in the solid state gave 4a of 44 % ee (96 % yield) or 4b of 59 % ee (57 % yield), respectively [4],... 

Wittig reactions of cyclohexanone derivatives in their inclusion compounds with the chiral host 5 gave optically active reaction products. For example, when a mixture of finely powdered 1 1 inclusion compound of 5b with 4-methyl-(15a) or 4-ethylcyclo-hexanone (15b) and phosphorane (16) was kept at 70 °C, the Wittig reaction in the solid state was completed within 4 h. To the reaction mixture was added diethyl ether-petroleum ether (1 1), and then the precipitated triphenylphos-phine oxide was removed by filtration. The crude product left after evaporation of solvent from the filtrate was distilled in vacuo to give (-)-4-methyl- (17a) of 42% ee (73 % yield) or (-)-4-ethyl-l-(carboethoxymethylene)cyclohexane (17b) of 45 % ee (57 % yield), respectively [9], Similar reaction of the 1 1 inclusion compound of 5c and c /. v - 3,5 - dime th y I c y c I o h e x a n o n e (18) with 16 gave 19 of 57 % ee in 58 % yield [9],... 

Solid state Wittig-Horner reaction of 4-methyl- (43a), 4-ethyl- (43b) and 3,5-di-methylcyclohexanone (44) as their inclusion complex with optically active host compound and (carbethoxymethylene)triphenylphosphorane (45) gave optically active 4-methyl- (46a), 4-ethyl- (46b) and 3,5-dimethyl-l-(carbethoxymelhy-lene)cyclohexane (47), respectively [16]. For example, when a mixture of the finely powdered 1 1 inclusion complex of 43a with 2b (1.5 g) and 45 (2.59 g) was kept at 70 C, the Wittig-Horner reaction was completed within 4 h. To the reaction mixture was added ether-petroleum (1 1) and the precipitated solid (Ph PO... 

The photocyclization of acrylanilide (122) to 3,4-dihydroquinolinone (123), which was first reported in 1971 [74], can also be carried out enantioselectively by using a chiral host compound. Irradiation of the finely powdered 1 1 inclusion complex of 122 with 26 in a water suspension gave (-)-123 of 98% ee in 46% yield [75]. By the same procedure, optically active 125, 127 and 129 were prepared from 124, 126 and 128, respectively (Table 15-23) [75]. 

Already, more than 25 years ago, Toda et al. reported the mechanochemical preparation of crystalline host-guest inclusion compounds and of charge-transfer (CT) systems. CT systems have also been studied by Kuroda et al., who were able to obtain multicomponent systems based on racemic bis-)8-naphtol, benzoquinone, and anthracene the cocrystal formation could be easily followed by the change in color of the solid mixtures. Importantly, this material was not accessible from conventional solution crystallization procedures and required structure determination from X-ray powder diffraction. ... 

The [2-1-2]-cycloaddition reactions in inclusion crystals, or host-guest crystals, have been thoroughly reviewed. Coumarin 61a, thiocoumarin 61b, and cyclohex-2-enone 62 efficiently undergo single-crystal-to-single-crystal enantioselective photodimerization in inclusion complexes with chiral host compounds (R,R)-(-)-fra s 63a, (R,R)- -)-trans 63b, and (-)-64, respectively. The products are (-)-anri-HH 65a (100% EE), +)-anti-HH 65b (100% EE), and -)-syn-trans 66 (48% EE) dimers. An example for enantioselective intramolecular [2+2]-photocycloadditions in inclusion crystals is the reaction of guest 67 in chiral host 68. Irradiation of the powdered inclusion crystals in water suspension affords the optically active photocyclization product 69 with 100% EE in 90% yield. 

The formation of such materials may be monitored by several techniques. One of the most useful methods is and C-nmr spectroscopy where stable complexes in solution may give rise to characteristic shifts of signals relative to the uncomplexed species (43). Solution nmr spectroscopy has also been used to detect the presence of soHd inclusion compound (after dissolution) and to determine composition (host guest ratio) of the material. Infrared spectroscopy (126) and combustion analysis are further methods to study inclusion formation. For general screening purposes of soHd inclusion stmctures, the x-ray powder diffraction method is suitable (123). However, if detailed stmctures are requited, the single crystal x-ray diffraction method (127) has to be used. 

It was found that efficient inclusion crystallization can be accomplished simply by mixing powdered crystalline host and a hydrophobic guest compound in hexane or water. By using the inclusion crystallization in suspension media, very efficient optical resolution method was established. Furthermore, when inclusion complexation between chiral host and rac-guest in the solid state is combined with a distillation procedure, optical resolution can easily be accomplished by the fractional distillation procedure. 

Successful complexation of the exchanged transition metals by the tetradentate ligand salen was indicated by the typical yellow/brownish colour of the prepared inclusion compounds. X-ray powder diffraction and scanning electron microscopy reveal that the crystallinity of the zeolite host is virtually retained during the modification steps. Furthermore, no crystals of the salen ligand or of metal-salen complexes are visible on the external surface of the zeolite crystallites after careful piuification via soxhlet extraction with acetone. Analysis of the used solvent by UVATS-spectroscopy revealed that only salen but no metal-salen complexes were removed from the zeolite during extraction. This indicates that the complexes are truly entrapped in the intracrystalline voids of the zeolite. It has been demonstrated [7] that the presence of salen and PdSalen in zeolite Y can be probed by IR-spectroscopy in... 

The powdered solids of host and guest were shaken for 1 min and kept at room temperature for 6 h to afford the 2 1 inclusion compound. 

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