Studies on a Novel Dehydrationg Gent, (Trimethylsilyl)ethoxyavetylene

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We have found that (trimethylasilyl)ethoxyacetlene (TMEA) provided a quire effective method for dehydration of various types of carboxylic acids, including acids-sensitive catboxylic acide into the corresponding carboxylic anhydrides under nmild conditions, and allowed easy isolation of pure products. These carboxylic anhydrides were successfully utilized for the strong base-induced cycloaddition to naphthoquinones leading to anthracyclines. We also succeeded in applying this carboxyl group activating method to the synthesis of amides.The following progress was made in the present project. We suvveeded in the first total sysnthesis of D-rind thiophene and indole analogues of daunomycin via a stronf-base induced cycloaddition of hterohomophthalic anhydride obtained by the use of TMEA. The reagent, TMEA was found to useful not only for amide formation but also for ewster, lactone, or non-racemized peptide formation. Next, we founs thar teimethylsilyl ketene (TMSK), readily prepared by heating of TMEA under reduced pressure, reacted with vatious types of alconhols to give the 1,2addition products, a-(trimethylsilyl)acetates in quantitative yield. The alcohol having carbonyl group in the moleuce similarly reacted with TMSK to give the corresponfding <alpha>-(trimethylsilyl)acetate, which caused an intramolcular pererson reaction to five <alpha>,<beta>-unsaturated lactone in excellent yield. We now try to find a novel annelation reaction using various types of <alpha>-(trimethylsilyl)acetates obtained by treatment of alcohols having some active functional gqoup with TMSK.