Tert-Butyldiphenylsilyl

In contrast to allylic phosphine oxides, phosphonates, sulfones and sulfoxides, the chemistry of lithiated allylic sulfoximines has been less extensively developed25 27. The reaction of lithiated racemic A-phenyl-A -(4-rnethylphenyl)-S -(2-propenyl)sulfoximine with either 2-cy-clopentenone or 2-cyclohexenone gave a complicated mixture with 1,4-oc-ad ducts being slightly favored over the 1,4-7-adducts. The yields of these adducts were poor25. In contrast, lithiated racemic Ar-tert-butyldiphenylsilyl-5-phenyl-5,-(2-propenyl)sulfoximine gives mainly 1,4-y-ad-ducts on reaction with the same enones26. 

Scheme 3.17 Ring-expansion using ROCM [TBDPS = tert-butyldiphenylsilyl]...

The sequence detailed here provides 3-(S)-((tert-butyldiphenylsilyl)oxy)-2-butanone in high purity and on a preparative scale from inexpensive (S)-ethyl lactate. This optically active ketone should be a useful intermediate for the preparation of a variety of enantiomerically pure materials. It has been used in our laboratory for an asymmetric synthesis of (+)-muscarine3 and in the preparation of various other optically active tetrahydrofurans.4 Mitsunobu inversion of (S)-ethyl lactate followed by protection to provide 2-(R)-((tert-butyldiphenylsilyl)oxy)propanoate5 affords, by this method, ready access to the enantiomer of the title compound. 

Ethyl 2-(S)-[(tert-butyldiphenylsilyl)oxy]propanoate Propanoic acid, 2-[[(1,1-dimethylethyl)diphenylsilyl]oxyJ-, ethyl ester, (S)- (11) (102732-44-5)... 

Tin-based reagents are not always snitable owing to the toxicity of organotin derivatives and the difficulties often encountered in removing tin residues from the final product. Therefore, the same authors have carried out additional experiments with 17d and several different alkyl halides under tin-free conditions. The treatment of 16d with tert-butyldiphenylsilyl chloride (TBDPSCl) and triethylamine in the presence of silver triflate in CH2CI2 affords the bis(silyloxy)enamine 17d in 92% yield (Scheme 17). When the radical reaction was carried out with ethyl iodoacetate in the presence of 2,2 -azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as the initiator in CH2CI2, the oxime ether 19 was obtained in 83% yield (Scheme 17). 

Akiyama et al. (180) overcame this problem by employing ch/ro-inositol derivatives as chiral auxiliaries for the acrylic ester, which afforded dipolar cycloadducts with a high degree of stereoselectivity (Scheme 6.34). Formation of the major products [(55)-isoxazoline-5-esters] was suggested to arise from the s-cis conformer of acrylate 27, the minor product being derived from the s-trans conformer 28. The bulky protective group (in this case tert-butyldiphenylsilyl) would effectively shield the Re face of the olefinic double bond and destabilize the s-trans conformer 28. 

The dependence of the acid-lability of trialkylsilyl and related ethers on the type of substitution at silicon is illustrated by the formation302 of l-0-(tert-butyldiphenylsilyl)-2,3 4,5-di-0-methylene-D-mannitol (47) in 96% yield on treatment of 6-0-(terf-butyldimethylsilyl)-l-0-(fert-butyldiphenylsilyl)-2,3 4,5-di-O-methylene-D-manni-tol (48) with 80% acetic acid. 

Sieber linker Su TBAF TBDPS TBS TBTU XAL linker, 3-alkoxy-9//-9-xanthenylamine IV-succinimidyl tetrabutylammonium fluoride tert-butyldiphenylsilyl tert-butyldimethylsilyl 3-[(dimethyliminium)(dimethylamino)methyl]-l,2,3-benzotria-zol-l-ium-l-olate tetrafluoroborate (Figure 13.6)... 

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