A ring expansion-annulation strategy for the synthesis of substituted azulenes. Preparation and Suzuki coupling reactions of 1-azulenyl triflates

[GRAPHICS] A new strategy for the synthesis of substituted azulenes is reported, based on the reaction of beta'-bromo-alpha -diazo ketones with rhodium carboxylates, The key transformation involves intramolecular addition of a rhodium carbenoid to an arene pi -bond, electrocyclic ring opening, beta -elimination, tautomerization, and trapping to produce 1-hydroxyazulene derivatives, The synthetic utility of the method is enhanced by the ability of the triflate derivatives to participate in Suzuki coupling reactions, as illustrated in a synthesis of the antiulcer drug egualen sodium (KT1-32).