Chiral alkyl groups

In the case of 67g which has a chiral alkyl group, optically pure 67g was included at the complexation process with 2a, and (—)-67g of 100% ee [[a]D —66.8° (c 0.22, CHClj)] was obtained. Irradiation of the 1 1 inclusion complex of 2a and (—)-67g of 100% ee gave 69g of 100% ee which has three optically pure chiral centers 40). This is not the result of a chiral induction by the optically active alkyl group, since irradiation of 67g of 100% ee in benzene gave 69g of only 12% de (diastereomeric excess). 

Advances in the use of anionic stereogenic phosphorus have been interesting. Acylation of lithium o-anisylphenylphosphide with chloro-formates bearing chiral alkyl groups provided a diastereomeric mixture that could be induced to undergo an inversion at phosphorus (at relatively low temperature) to form the more favorable diastereoisomer in a crystalline lattice.186 Subsequent conversion to the quaternary phos-phonium species was followed by removal of the acyl group and isolation of the chiral tertiary phosphine as the borane derivative (Equation 3.10). 

The Gabriel synthesis is a classical but useful preparative method for primary amines. Reaction of an alkyl bromide (24) with potassium phthalimide (25) gives the corresponding A -alkylphthalinude (26), which upon treatment with hydrazine followed by KOH affords the primary amine (27). When a chiral alkyl halide is used in the Gabriel synthesis, a chiral primary amine is obtained. However, preparation of optically active alkyl halides is not easy. If optical resolution of 26 which has a chiral alkyl group can be done, a new preparative method for optically active amines can be established by a combination of the resolution with the Gabriel synthetic method. Some examples of the combination method are described. 

Recently we found that the chiral alkyl group bonded to the cobalt atom in a cobaloxime complex crystal is almost (82%) inverted to the opposite configuration only by photoirradiation [12]. In this chapter we describe the processes of the racemic-to-chiral transformation and also the chirality inversion in the... 

Such crystalline-state racemizations by photoirradiation were observed in the cobaloxime complexes not only with the chiral 1-cyanoethyl group but also with the chiral l-(methoxycarbonyl)ethyl [18-20], 1-(ethoxycarbonyl)ethyl [12,21], 1,2-bis(methoxycarbonyl)ethyl [22], l,2-bis(ethoxycarbonyl)ethyl [23], and l,2-bis(allyloxycarbonyl)ethyl [24] groups as axial alkyl groups. The concept of a reaction cavity was also applicable to the racemization of the cobaloxime complexes with such bulky chiral alkyl groups. 

There have been many papers concerning liquid-crystalline polymers having azobenzenes in their side chains (Figure 14) because of the mesogenic nature of the azo chromophore. Liquid-crystalline polymers incorporating azobenzene moieties in their main chains (30) have also been prepared.102 A family of poly(acrylates) substituted with azobenzenes having chiral alkyl groups (31) showed smectic A as well as cholesteric phases.103 The photochromic behavior... 

R = chiral alkyl group R1 = achiral alkyl group... 

Firstly, the optical purity of alkylmono- and alkyldiisopinocampheylboranes with a chiral alkyl group can often be increased to essentially 100% ee by crystallization84. 

R — chiral alkyl group R1, R2 = achiral alkyl groups... 

To observe the intermediate structures one must collect the intensity data rapidly. We designed and made a diffractometer, R-AXIS lies, for rapid collection [7] of data, which has been marketed in a revised form by Rigaku Company as R-AXIS RAPID since 1998. The two-step crystalline-state reaction was first found in the inversion of a chiral alkyl group bonded to the cobalt atom in a cobaloxime complex when the crystal on the diffractometer was irradiated with a xenon lamp [8]. Figure 5-2 shows the two-step structural change of the complex, ((R)-l-methoxy-carbonylethyl) [(S)-l-phenylethylamine] cobaloxime. After exposure for 2h, the structure (Figure 5-2b) showed the disordered structure of the chiral (R)-... 

When insertion of the coordinated prochiral olefin to a metal alkyl or a metal hydride takes place, the stereochemistry of the substituted carbon atom is determined as either R or S enantiomer. When the chiral alkyl group is reductively eliminated with the hydrido ligand, asymmetric hydrogenation of an olefin producing enatiomeric excess of one of the optical isomers can be achieved. 

In this study, we designed and synthesized a series of novel PMP derivatives with chiral groups as side chains, (/f)-/(S)-Poly-l (Fig. 11.2) [10]. Poly-1 features a chiral side chain with either (/ )- or (S)-2-nonanol chiral alkyl groups linked via... 

Here, we have designed and synthesized multifunctional poly(bithienylene-phenylene)s with either racemic (Poly-9) (M — 14,000) or chiral moieties ((/ )-/ (S)-Poly-lO (Mn = 10,000, 8,000, respectively), which exhibit fluorescence, liquid crystallinity, and photoresponsive properties (Fig. 11.20). The polymers are composed of a 7t-conjugated main chain, poly(bithienylene-phenylene), which acts as a fluorescence moiety and mesogen core, and photochromic DE moieties [71, 72] are linked with racemic or chiral alkyl groups in the side chains. The DE photoresponsive moiety isomerizes between its closed and open forms upon irradiation of UV and visible light, respectively. 

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