A concise synthetic route to diverse acyclic and heterocyclic compounds has been developed by combining hetero‐Diels–Alder reactions, DBU‐promoted ring openings, and Lewis base‐catalyzed annulations. Nitrosoalkenes reacted with furan derivatives to form 4a,7a‐dihydro‐4 H ‐furo2,3‐ e 1,2oxazines, which underwent DBU‐promoted rearrangements to 6 H ‐1,2‐oxazines and 2‐acetylpyridines. Subsequent DABCO‐mediated reaction of 6 H ‐1,2‐oxazines with allenoates afforded conjugated polyenes and dihydropyrans with excellent regio‐ and stereoselectivity. This chemistry applied to bis‐furans led to novel furan hybrids and furan derivatives bearing 6 H ‐oxazine, pyridine, polyene, dihydropyran, and 4 H‐ pyran motifs—recognized as privileged structures in medicinal chemistry—through the selective modification of one of the two furan units.
Cardoso et al. (Mon,) studied this question.