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Perhydrotriphenylene, crystal lattice

BINAP, 127, 171, 191, 194, 196 olefin reaction, 126, 167, 169, 191 organic halides, 191 Pancreatic lipase inhibitors, 357 Pantoyl lactone, 56, 59 para-hydrogen, 53 Peptides, matrix structure, 350 Perhydrotriphenylene, crystal lattice, 347 Pericyclic reactions, 212 chiral metal complexes, 212 Claisen rearrangement, 222 Diels-Alder, 212, 291 ene reaction, 222, 291 olefin dihydroxylation, 150 Phase-transfer reactions asymmetric catalysis, 333... [Pg.196]

The characteristic of crystal lattices is a strict periodical succession of structurally identical molecular units, in the sense of an inclusion lattice also of holes, channels, layers etc. which may include guest molecules in an oriented fashion. This organizing principle makes topochemistry possible. One of the early studies in this area was the inclusion polymerization of dienes in the channels of urea, respectively thiourea, leading to stereoregular polymers (Eq. 1) Although stereodifferentiating inclusion polymerization/co-polymerization has been performed in other host lattices, too, e.g. in the channels of the perhydrotriphenylene host (6) it is still a problem of actual interest... [Pg.10]

A novel example of an asymmetric synthesis in which a prochiral diene monomer is included in the crystal lattice of a chiral host compound which can form an optically active polymer on 7-ray irradiation was reported by Farina et al [208]. By irradiation of trans-1,3-pentadiene (LXXIX) included in ( XT )- or (+)(,S )-perhydrotriphenylene (LXXIX) of trans-anti-trans-anti configuration in the solid state, isotactic OA polymers, of opposite sign, were obtained the rotatory powers are weak but unambiguous. [Pg.75]

There are several alternative methods for the synthesis of optically active polymers from achiral or racemic monomers that do not involve polymerization catalysts. Optically active polymers have been formed from achiral dienes immobilized in a chiral host lattices [ 106]. In these reactions, the chiral matrix serves as a catalyst and can be recovered following the reaction. For example, 1,3-penta-dienes have been polymerized in perhydrotriphenylene and apochoUc acid hosts, where asymmetric induction occurs via through-space interactions between the chiral host and the monomer [107,108]. The resultant polymers are optically active, and the optical purities of the ozonolysis products are as high as 36%. In addition, achiral monomers have been found to pack in chiral crystals with the orientations necessary for topochemical soHd-state polymerization [109]. In these reactions, the scientist is the enantioselective catalyst who separates the enantiomeric crystals. The oligomers, formed by a [27H-27i] asymmetric photopolymerization, can be obtained in the enantiomeric pure form [110]. [Pg.1271]

Pure tra i-l,4-polyisoprenes as well as 1,4-polybutadienes can be synthesized by polymerization in inclusion compounds [266-269]. As typical hosts for this dienes, the inclusion compounds or clathrates of urea, thiourea, or perhydrotriphenylene [PHTP Eq. (36)] are used [270,271]. The host forms the frame of the crystal and the guest is placed in the cavities existing in the lattice. Polymerization is generally started by subjecting the inclusion compound to irradiation with a-, y-, or x-rays and proceeds by a radical mechanism [272,273]. Also, free radical initiators such as di-/cr/-butylperoxide could be used [274]. Inclusion in urea yields crystalline trans-, A polymers, whereas trans-lA-polyisoprene obtained in PHTP is amorphous. There is no trace of, A-cis units or of 1,2, 3,4, and cyclic units. The reason for the amorphous product is the presence of a substantial number of head-to-head and tail-to-tail junctions in addition to head-to-jail junctions [275, 276]. [Pg.355]


See other pages where Perhydrotriphenylene, crystal lattice is mentioned: [Pg.3449]    [Pg.81]    [Pg.20]    [Pg.25]   
See also in sourсe #XX -- [ Pg.347 ]




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Perhydrotriphenylene

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