61145-17-3Relevant academic research and scientific papers
Hetero-Diels–Alder and Ring-Opening Reactions of Furans Applied to the Synthesis of Functionalized Heterocycles
Alves, Américo J. S.,Lopes, Susana M. M.,Henriques, Marta S. C.,Paix?o, José A.,Pinho e Melo, Teresa M. V. D.
, p. 4011 - 4025 (2017/07/28)
Furans have been explored as a scaffold for the synthesis of a range of heterocyclic compounds, exploring their dienophilic behaviour towards nitroso- and azoalkenes as the first step. Acid-catalysed rearrangements of these cycloadducts, 4a,7a-dihydro-4H-furo[2,3-e][1,2]oxazines and 1,4,4a,7a-tetrahydrofuro[3,2-c]pyridazines, were studied. Using 1 equiv. of TFA, the bicyclic heterocycles derived from furan and 2-methylfuran were converted into furans bearing side-chains incorporating oxime and hydrazone groups by ring-opening of the six-membered ring with the concomitant aromatization of the furan ring. The use of TFA as solvent led to rearrangement via spirocyclic intermediates, followed by furan ring-opening to afford functionalized isoxazoles or pyrazoles. Furthermore, furo-oxazines derived from 2,5-dimethylfuran, in which furan aromatization is precluded, were converted efficiently into 6H-1,2-oxazines through a furan ring-opening reaction upon thermolysis in the presence of a catalytic amount of p-toluenesulfonic acid. The tetrahydrofuro[3,2-c]pyridazines derived from furan and dimethylfuran underwent acid-catalysed addition reactions, leading to 6-substituted hexahydrofuro[3,2-c]pyridazines, when in the presence of alcohols or water.
