S-butyl group

The yields of dialkylacetates are 74-82% when R and R are combinations of n-, iso-, and s-butyl groups. This interesting cleavage has been used to prepare ethoxy esters from ethoxy halides of the type CjHjOfCHjl jX as well as a-methyladipic ester from the corresponding cyclic /3-keto ester (83%). ... 

Asymmetric Synthesis in the Racemic System.—Once we had a suitable model system, we moved to the next step of the planning, which required the construction of a crystalline phase isomorphous to (2), but composed of non-chiral molecules or a racemic mixture of molecules. One possible solution to this problem came from the observation that the crystals of many compounds containing the chiral s-butyl group have a strong tendency to disordering about the chiral centre (see Section 4, p. 218). When this is the case, the resolved enantiomer and its racemate generally pack in isostructural crystals. 

Contacts between the chiral s-butyl and other residues in its environment were considered as well. Figure 6 illustrates the contacts between the s-butyl group of a molecule sitting at (0,0,0) and the ethyl ester groups of the two neighbouring molecules at (1,2,1) and (1,T,1) at distances of 3.9 and 3.8 A away, respectively. A transfer of... 

The s-butyl group can adopt a range of conformations in the crystal. For example, resolved s-butyl 2,3-anthroate crystallizes in space group C2 with four crystallographi-cally independent molecules in the unit cell, and each independent s-butyl group adopts a different conformation (Figure 8). ... 

Thus both configurational disorder of the s-butyl group and the isomorphism between enantiomeric crystals and their racemic counterparts occur by virtue of the following molecular property a s-butyl group is able to occupy almost the same space occupied by its enantiomer by a change in conformation and position. We may define this property as conformational isomorphism. ... 

Butane yields the butyl and s-butyl groups, the former by removal of a hydrogen from one of the end carbons and the latter by removal of a hydrogen from one of the inner carbons. 

Optical properties of cyanines can be usefiil for both chiral substituents/environments and also third-order nonlinear optical properties in polymer films. Methine-chain substituted die arbo cyanines have been prepared from a chiral dialdehyde (S)-(+)-2-j -butylmalonaldehyde [127473-57-8] (79), where the chiral properties are introduced via the chiral j -butyl group on the central methine carbon of the pentamethine (die arbo cyanine) chromophore. For a nonchiral oxadicarbocyanine, the dimeric aggregate form of the dye shows circular dichroism when trapped in y-cyclodextrin (80). Attempts to prepare polymers with carbocyanine repeat units (linked by flexible chains) gave oligomers with only two or three repeat units (81). However, these materials... 

The limitations of the system with regard to substrates and oxidants was attributed to the strong electron-withdrawing character of the perfluorinated chains and the lower steric hindrance in the position adjacent to phenols, in marked contrast to the ferf-butyl groups present in Jacobsen s catalyst, hi view of this, a second generation of fluorinated salen ligands le and If was... 

Carbanions derived from optically active sulfoxides react with esters, affording generally optically active )S-ketoesters ° . Kunieda and coworkers revealed that treatment of (-t-)-(R)-methyl p-tolyl sulfoxide 107 with n-butyllithium or dimethy-lamine afforded the corresponding carbanion, which upon further reaction with ethyl benzoate gave (-l-)-(R)-a-(p-tolylsulfinyl)acetophenone 108. They also found that the reaction between chiral esters of carboxylic acids (R COOR ) and a-lithio aryl methyl sulfoxides gave optically active 3-ketosulfoxides The stereoselectivity was found to be markedly influenced by the size of the R group of the esters and the optical purity reached to 70.3% when R was a t-butyl group. 

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