Abstract
A range of double unsaturated amides ( 15 , 19 , and 21 ), obtained by cross-coupling reactions was reacted with aldehydes to hemiaminals. Heating the hemiaminals in the presence of Ac 2O and pyridine affected clean conversion to the corresponding enamides, such as 42 , 45 , and 47 . Alternatively, N,S-acetals were prepared which were oxidized to the sulfones. Treatment with base also gave the enamides, favoring the cis-isomer. However, this method is less general. Application of these methods led to the natural products lansiumamide-A ( 30_ cis ), lansiumamide-I ( 31 ) and lansiumamide-B ( 32 ).
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