REACTIONS OF GUAIAZULENE WITH ALDEHYDE RE AGENTS IN ACETIC-ACID - AN EFFICIENT PREPARATION OF 3,3'-METHYLENEDIGUAIAZULENE DERIVATIVES

The reaction of guaiazulene (1) with a 1.3 molar amounts of an aldehyd e reagent (i.e., acetaldehyde, benzaldehyde, glyoxal, glyoxylic acid, and furaldehyde) in acetic acid at room temperature (25 degrees C) for 1-4 h under argon readily gave the corresponding 3,3'-methylenediguai azulene having a substituent at C-rr position (2, 3, 4, 5, and 6, resp ectively) in good yield (83-98%). A rearrangement product, trans-4,5-d i-(3-guaiazulenyl)-2-cyclopenten-1-one (7), was also obtained as a min or product (8% yield) by the reaction of 1 with furaldehyde. The struc tures of these products were established on the basis of their spectro scopic (UV/VIS, MS, IR, and NMR) data. Possible reaction pathways for the formation of these compounds are discussed.