Abstract
A straight forward synthetic protocol for spiro and fused chromenes has been developed by base promoted oxa-Michael/Mannich reaction of salicyl N-tosylimines and various cyclic dienophiles. 1,4-diazabicyclo[2.2.2]octane (DABCO) promoted [4 + 2] cycloaddition reaction of salicyl N-tosylimines and 3-methyleneoxindoles or 2-arylidene-1,3-indanediones in THF at room temperature afforded functionalized spiro[chromane-3,3′-indolines] or spiro[chromane-3,2′-inden]-1′,3′-diones in moderate to good yields and with high diastereoselectivity. On the other hands, the similar [4 + 2] cycloaddition of salicyl N-tosylimines and 5,6-unsubstituted 1,4-dihydropyridines resulted in tetrahydrochromeno[3,2-b]pyridine derivatives in satisfactory yields.
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