Regioselective reductive ring opening of 2-(2-hydroxyphenyl)-3-[(trimethylsilyl)oxy]oxetanes at the more substituted C-2 position

The title compounds 7 were prepared in situ by deprotection of the corresponding pivaloyl-substituted oxetanes 3 with lithium aluminium hydride in tetrahydrofuran. Under these conditions a reductive ring opening at C-2 (hydrodealkoxylation) occurred which was initiated by a nucleophilic hydride attack and which yielded the triols 8 (64-85%). The facility of the reaction and its high regioselectivity can be explained by the directing ability of the hydroxy group at the aromatic substituent. The reaction proceeds stereospecifically, as shown by deuterium labelling experiments. The prerequisite 2-(2-pivaloyloxyphenyl)-3-[(trimethylsilyl)oxy]oxetanes 3 were prepared by the Paternò-Büchi reaction of the protected salicylaldehyde 1 and various silyl enol ethers 2. The 2-hydroxyphenyl substituent at the C-3 position of oxetane 6 directed the hydride attack to the C-4 position and yielded the triol 10 in 85% yield.