T -butyl group

This will clearly be made somehow by discormections a and b but the order of events is important. We must discoimect first, that is synthesise last, the bond with the wrong orientation - i.e. meta to the t-butyl group. The reaction will then be intramolecular and orientation doesn t matter. This gives us 399B, and 1 show one possible route from that. 

In the following example the acetonide protective group is selectively converted to one of two t-butyl groups. The reaction appears to be general, but the alcohol bearing the t-butyl group varies with structure.Benzyli-dene ketals are also cleaved. 

These various photoproducts are all valence isomers of the normal benzenoid structure. These alternative bonding patterns are reached from the excited state, but it is difficult to specify a precise mechanism. The presence of the t-butyl groups introduces a steric factor that works in favor of the photochemical valence isomerism. Whereas the t-butyl groups are coplanar with the ring in the aromatic system, the geometry of the bicyclic products results in reduced steric interactions between adjacent t-butyl groups. 

A study of the photolysis of A, B, and C has been reported. A gives both D and the cleavage product benzaldehyde. B gives only E. C gives benzaldehyde and the stereoisomer B. Discuss the ways in which the presence and configuration of the remote t-butyl group can control the product composition, and account for the formation of the observed products. 

Interestingly the pyrrolidine enamine of 3-t-butylcyclohexanone (41) consists of a 3 2 mixture of A and A isomers (79 and 80). The preference for the A isomer in this case is due to the relief of two of the four skew butane interactions, which are present in the isomer. The A isomer, owever, contains two additional interactions, i.e., one modified skew utane interaction 0.4 kcal/mole (42) and one interaction between c C-2 vinylic hydrogen atom and the ethyl portion of the t-butyl group hich is pointed toward it. 

The first objective was the conversion of L-tryptophan into a derivative that could be converted to pyrroloindoline 3, possessing a cis ring fusion and a syn relationship of the carboxyl and hydroxyl groups. This was achieved by the conversions shown in Scheme 1. A critical step was e. Of many variants tried, the use of the trityl group on the NH2 of tryptophan and the t-butyl group on the carboxyl resulted in stereospecific oxidative cyclization to afford 3 of the desired cis-syn stereochemistry in good yield. 

In contrast with 69, molecules of benzotelluradiazole 75 in the solid state are associated in dimers rather than polymeric chains. The bulky t-butyl groups of 75 prevent a higher degree of association and provide for good solubility of 75, which readily crystallizes from its pentane solution. 

The striking simplicity of the methacrylate polymerization caused by the introduction of a t-butyl group was noted also in anionic polymerization of related monomers such as t-butyl acrylate57), t-butyl crotonate 58) and t-butyl vinyl ketone. 

A. Preparation and Structure.—-A study of the i.r. and Raman spectra of t-butyltetrafluorophosphorane (34 n = 1) has indicated that it is a trigonal bipyramid with the t-butyl group equatorial. The preparation... 

Trippett and Stewart have shown that the phosphonium salts (11) derived from the reaction of phenyl di-t-butylphosphinite (12) with alkyl halides are highly resistant to hydrolysis and they suggest that this is due to the reluctance of phosphorus to accommodate two t-butyl groups in a trigonal-bipyramidal intermediate. 

Similar results were obtained from a study of 2-phenyl-5-t-butyl-l,3 2-dioxaphosphorinane (111) in that the cw-isomer was thermodynamically more stable than the trans. However, in this case even the trans-isomer adopts a conformation (112) with the P-phenyl group and, perforce, the t-butyl group axial. A similar situation has already been noted in the phosphite (108), and it may be that the special case of a phenyl group produces some type of pseudo anomeric effect. 

Alkyl monoesters of thiophosphoric acid have not hitherto been readily accessible compounds owing to indifferent yields and lengthy and difficult isolation procedures. A simple preparative route involves reaction of OO-di-t-butyl hydrogen phosphorothioate with the appropriate alkyl halides followed by elimination of the t-butyl groups with dry hydrogen chloride in dichloromethane ... 

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. 

Figure 7.18. (a) ORTEP representation of radical 41, and the stereoview of the crystal packing, with out the t-butyl groups, (b) ORTEP representation of radical 42, and the packing arrangement viewed along the c-axis to show the trkneric interactions. (Adapted from refs. 107 and 108.)... 

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