Synthetic studies of substituted pyridine aldehydes as intermediates for the synthesis of toddaquinoline, its derivatives and other natural products

The synthesis of substituted 2-bromopyridine aldehydes as intermediates in our planned approach to toddaquinoline, its derivatives and other natural products is reported. The DMF-formylation method of pyridine ring, the Vilsmeier-Haack procedure and the bromination of pyridine ring respectively, were studied in order to synthesize the above mentioned compounds. The successful methods (DMF-formylation and bromination of pyridine ring) provided the 2-bromo-4-formyl-5-tosyloxypyridine Ib and 5-benzyloxy-2,4,6- tribromonicotinaldehyde Ia under relatively mild conditions and in good yields.