SODIUM BIS(TRIMETHYLSILYL)AMIDE AND LITHIUM DIISOPROPYLAMIDE IN DEPROTECTION OF ALKYL ARYL ETHERS - ALPHA-EFFECT OF SILICON

Removal of methyl, benzyl, and methylene groups from alkyl aryl ethers is among the most popular deprotecting methods in organic synthesis. Alkali organoamides NaN(SiMe3)(2) and LiN(i-Pr)(2), often used as orga nic bases, have been developed as efficient deprotecting agents. Treat ment of aryl methyl ethers with 1.5 equiv of NaN(SiMe3)(2) or LiN(i-Pr )(2) in THF and 1,3-dimethyl-2-imidazolidinone in a sealed tube at 185 degrees C produced the corresponding phenol derivatives in good to ex cellent yields (80-97%). Removal of the methylene unit from benzodioxo le derivatives was also accomplished by use of 2.5 equiv of these alka li organoamides. The corresponding catechols were obtained in 93-99% y ields. The activity of NaN(SiMe3)(2) was proven lower than that of LiN (i-Pr)(2); it is due to the steric congestion and the alpha-stabilizin g effect of the silyl groups. Thus selective mono-O-demethylation of o -dimethoxybenzenes can be achieved by the use of NaN(SiMe3)(2) but not LiN(i-Pr)(2). O-Debenzylation of aryl benzyl ethers, however, can be accomplished by the use of LiN(i-Pr)(2).