Allylic alcohols, 0-silyl protected

The allylic alcohol is protected as a silyl ether under basic conditions. 

Scheme 3.34. Intermolecular domino radical addition procedure for the synthesis of silyl-protected allylic alcohols.

Decarboxylation of 117 was effected by treatment of 117 with LiCl in hot, aqueous HMPA at 105 °C providing 118 as a mixture of diastereomers that were separated and carried forward individually. Protection of the secondary amide group as the corresponding methyl lactim ether was accomplished by treating 118 with trimethyloxonium tetrafluoroborate in dichloromethane that contained cesium carbonate. Next, the indole nitrogen atom was protected as the corresponding Boc derivative by treatment with dicarbonic acid bis(rm-butyl)ester in the presence of DMAP and the silyl ether was removed with tetrabutylammonium fluoride to provide diol 119 in 52-78% overall yield from 118. Selective conversion of the allylic alcohol to the corresponding... 

Two recently developed coupling reactions of an alkene (R1CH2CH=CH2), an aldehyde (R2CHO), and a silyl triflate (R33SiOTf) yield an allylic (66) or homoallylic (67) alcohol (in protected form).188 Employing nickel-phosphine catalysts, either product can be selected by small changes in the phosphine component. A mechanism distinct from that of Lewis acid-catalysed carbonyl-ene reactions is proposed and discussed. 

Silylmethyl oxetanes were converted to allylic alcohols when added to a solution of tetrabutylammonium fluoride (TBAF) in THF (Equation 15) <1998JOC5517>. Treatment with TBAF is a commonly known method of removing silyl protecting groups. In this case, attack of the fluoride ion on the silica atom lead to elimination of the silyl group and ring opening of the oxetane. 

Allylic alcohol 129 can be protected as a silyl ether and then subjected to the Sharpless asymmetric dihydroxylation giving other alditol stereomers. The latter can be converted into all kinds of C5-monosaccharide derivatives. An example is given in Scheme 13.49 [91]. 

Silyl-protected allylic alcohols can be obtained by treatment of epoxides with a non-nucleophilic base in the presence of stoichiometric amounts of TMSOTf or TBSOTf (Tf =S02CF3). ... 

The reaction has been investigated with MeOH, - z-PrOH, - t-BuOH, " phenols, " cyclic allylic alcohols, - homoallylic alcohols, 3,4-hydroxybenzoate, and mono Z-butyldimethyl-silyl protected diols. A subsequent Homer-Wadsworth-Emmons olefination with a range of aldehydes affords the corresponding enol ethers. ... 

The required chain extension of 12 was accomplished via deprotonation with NaH and condensation with aldehyde 7 to afford the Diels-Alder precursor 13 in 50% yield. Thermolysis of triene 13 and lactam 3 in xylene at 170 C for four days resulted in the desired cycloaddition to 14. Chromatographic purification permitted isolation of pure 14 in addition to a small amount of an exo isomer (>4 1 ratio). Acid treatment induced cleavage of both the silyl ether and acetonide. Reprotection of the diol and selective epoxidation of the A olefin produced 15 in 64% yield from 12. Epoxide 12 was then transformed to the isomeric allylic alcohol 16 by conversion of the alcohol to the bromide followed by reductive elimination. Protecting-group manipulation and subsequent oxidation the gave aldehyde 17, which was homologated and hydrolyzed to give seco acid 18 in 32% overall yield from 16. 

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