Silyloxyquinolinium salts

Diastereoselective Synthesis of Annulated Quinolones by Transformations with 4-Silyloxyquinolinium-Salts... 

Summary A new and efficient method for the highly diastereoselective annulation of 4-quinolones using 4-silyloxyquinolinium-salts is presented. Reactions of the quinolinium-salts with several 2-silyloxy-l,3-butadienes give cis-cis fused acridones with yields of 62-99 %. 

Amuilations of pyridinium- and quinolinium-salts however have not been reported so far. From the addition reactions of C-nucIeophiles like Grignard, organozinc and organotin reagents to pyridinium- and quinolinium-salts have been reported to be valuable methods for the construction of substituted dihydropyridine [4a-4d] and dihydroquinoline-derivatives [4d-4e] results of our studies in the field of benzothiopyrylium-salts [5] we concluded that the sequential intermolecular 1,2-addition/intramolecular 1,4-addition of 4-silyloxyquinolinium-salts 1 with 2-silyloxy-l,3-butadienes 2 might be useful for the diastereoselective preparation of annulated quinolones 3. 

As expected, the reaction of the 4-silyloxyquinolinium-salt 1, which can be regarded as a double activated 4-quinolone, with the unsubstituted 2-silyloxy-l,3-butadiene 2 diastereoselectively gives the cis-flised acridone 5 with 86 % yield. 

A great advantage of the new method is that both reactants, the double activated 4-silyloxyquinolinium-salt 1 and the 2-silyloxy-l,3-butadiene 2 [6], are obtained in situ from the corresponding 4-quinolone 6 and methyl vinyl ketone 7 by reaction with triisopropylsilyltrifluoro-methanesulfonate (TIPSOTf) and TIPSOTfy2,6-lutidine, respectively. 

Reaction of the 4-silyloxyquinolinium-salt 1 with the 3,4>disubstituted 2-silyloxybutadiene 8 exclusively yields the cis-cis annulation product 9 with excellent yield. Again, both reactants are formed in situ in one flask. First, the 4-silyloxyquinolinium-salt 1 is obtained from the quinolone 6 by treatment with TIPSOTf and then subsequently the 2-silyloxybutadiene 8 is formed fix)m 1-acetylcylopentene [7] by reaction with TIPSOTf and 2,6-lutidine. 

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