Silylether cleavage

A similar result was reported by Vandewalle 15°-151>. Irradiation of 1,2-bis(tn-methylsiloxy)cyclobutene and compounds (441) afforded compounds (442), which were reduced with LiAlH4 to give the endo alcohol (443). Treatment of the alcohol (443) with methanol for 24 hours would bring about silylether cleavage as well as unexpected direct oxidation of (443) to the cis-hydrindanes (444) in 50-70 % yield (Table 18)130). 

Under these conditions cycloheptene derivative 35 also reacts [15]. After cleavage of the silylether, cyclic hydroxy ketone 37 can be isolated in 95 % yield and 71 % ee. 

To access 5a-carba-L-gulopyranose derivatives 119 and 121, Stork cyclization clearly transformed cyclohexene 116 into cyclic silylether 117 which, after oxidative cleavage of the C-Si bond, led to 118, the direct precursor of p-L-configured carbahexose 119. The a-L-anomeric counterpart 121 was obtained from the common intermediate 118 by a short sequence centered upon inversion of configuration of the pseudoanomeric carbon. Inversion of the configuration at Ci in 116 and application of the same protocol ensured preparation of both anomers of the D-talo-configured carbasugars. 

The disilyl derivative of all-cix-1,2-epoxycyclopentane-3,5-diol 5 7 was treated with diethyloctynylalane to afford after cleavage of the silylether function the triol 58. This triol was convered via the acetonide to the benzyl ether 59. Hydrolysis with aqueous trifluoroacetic acid yielded the diol benzylether 60 which could be prepared by an alternative route as well. This route proceeds via the monotrityl epoxide 61 and benzylation to the trityl benzylether 62 and then reaction with diethyl octynyl alane to the diolbenzylether 60 and the isomeric 1,3-diol. 

In order to determine suitable deprotection conditions, silyl ethers of -butanol, 2-butanol, cyclohexanol, terf-butanol and phenol were synthesized. Table 2 shows various reaction and cleavage conditions that are commonly used in desilylation reactions for secondary alcohols. The progress of the reaction was analyzed using GC techniques and compared to a blank sample. For direct comparison, the corresponding silylethers of too-propyldimethylsilyl (8, IPM2) and TBM2 10 were treated in the same way as the NM2 silyl ether 9. 

---