Exploring the Chemistry of Furans: Synthesis of Functionalized Bis(furan‐2‐yl)methanes and 1,6‐Dihydropyridazines

The reactivity of 2,2‐bis(furan‐2‐yl)propane towards nitroso‐ and azoalkenes was explored. The expected hetero‐Diels–Alder adducts, 4a,7a‐dihydro‐4H‐furo[2,3‐e][1,2]oxazines and 4a,7a‐dihydrofuro[3,2‐c]pyridazines, were obtained in good yield. The furo‐oxazines were easily converted into the corresponding bis(furan‐2‐yl)methanes bearing an open‐chain oxime. Interestingly, the synthesized furo‐pyridazines showed a different chemical behavior. In the presence of HCl, they underwent a rearrangement giving 6‐(2‐oxobutyl)‐1,6‐dihydropyridazine derivatives in a process having as its key step a furan ring‐opening reaction. The synthesis of 4a,7a‐dihydrofuro[3,2‐c]pyridazines from 2‐methylfuran and the subsequent acid‐catalysed rearrangement to the corresponding 6‐(2‐oxopropyl)‐1,6‐dihydropyridazines was also achieved.