Molecular Transformation of 2‐Methylazulenes: An Efficient and Practical Synthesis of 2‐Formyl‐ and 2‐Ethynylazulenes

다국어 초록 (Multilingual Abstract)

2‐Formylazulene derivatives have been obtained in good yields by the reactions of 2‐methylazulenes with N,N‐dimethylformamide dimethyl acetal, followed by oxidative cleavage of the intermediately formed enamines with NaIO4. Vilsmeier formylation of 1‐phenyl‐3‐methylazulenes also afforded the corresponding 2‐formylazulenes in moderate yields. The treatment of a 2‐methylazulene derivative bearing a formyl group at the 1‐position with sodium methoxide led, through a self‐condensation reaction, to a trans‐1‐(azulen‐1‐yl)‐2‐(azulen‐2‐yl)ethylene derivative, the structure of which was verified by single‐crystal X‐ray diffraction analysis. The 2‐formylazulenes obtained were transformed into 2‐ethynylazulenes in good yields by a modified Seyferth–Gilbert reaction. The reactivity of a 1‐iodoazulene bearing a 2‐formyl function in palladium‐catalyzed cross‐coupling reactions has also been examined.
2‐Formylazulene derivatives have been obtained in good yields by the reactions of 2‐methylazulenes with N,N‐dimethylformamide dimethyl acetal, followed by oxidative cleavage of the intermediately formed enamines with NaIO4. The 2‐formylazulenes obtained were transformed into 2‐ethynylazulenes in good yields by a modification of the Seyferth–Gilbert reaction.