A New Method for High Activation of Acyliminium Ions and Reactions with Group 14 Organometallic Reagents

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Development of methodology for introduction of useful functional carbon substituents into nitrogen heterocycles is of great importance of synthesis of various physiologically and pharmacolotically active nitrogen heterocyclic compounds.It has been found in the studies during 1996 that a highly activated N-acylquinolinium ion is generated when quinoline is treated with phenyl chloroformate and silver triflate and that N-ccylquinoliun ion thus pwoduced can readily react with allylsilanes. It has been found, furthermore, that the similar reaction of isoquinoline with allylsilane to the above affords a benzoisoquinuclidine system.On the basis of the above results, major purposes in this year are focused on improvements of the reaction conditions as well as the reactions by means of other organosilicon reagents than allylsilane in order to introduce other useful carbon substituents than allyl group into nitrogen heteroaromatics.A variety of functional groups, such as ester, formyl, cyano, a … More nd nitro, on heteroaromatics are tolerated in the present reaction, showing the high chemoselectivity, though the yields are low in some cases. After the through experiments, acetnitrile has been found to the better solvent than dichloromethane, increasing the yields in almost all of the reactions. This could be ascribed to a favorable formation of N-acyl-quinolinium ion in more polar acetonitrile solution. Use of non-chlorinated solvent is another advantage from environmental point of view. The reactions with 2-methyl-, 2-chloromethyl-, and 2-trimethysiloxy-methylallylsilanes also readily proceed to give adducts in good yields. The reactions of beta-carboline system also work very well.Next, the reactions with allenyl-, propargyl-, and alkynylsilanes have been examined. It has been found that the reactions with allenylsilanes in the presence of equimolar amount of silver triflate in acetnitrile gives propargylated adducts in good yields. The reactions with propargylsilanes in presence of catalytic amount of silver triflate afford allenylated adducts in good yields. Furthermore, the reactions with less reactive alkynylsilanes are conducted in the presence of equimolar amount of silver triflate at elevated temperature to give alkynylated adducts in goond yields. Less