USE OF FUNCTIONALIZED YNAMINES IN A HETERO-DIELS-ALDER APPROACH TO DIHYDRONAPHTHO[1,2-B]PYRANS AND INDENO[1,2-B]PYRANS

Reaction of the ynamine ester methyl 3-(pyrrolidin-1-yl)prop-2-ynoate 5 with 2-(4-nitrobenzylidene)-1-tetralone 1 results in a very poor yie ld of the chromatographically labile 4-aryl-5,6-dihydro-4H-naphtho[1,2 -b]pyran 8 along with the alpha-pyrone 10. Increasing the reactivity o f the 4pi component by using the 2-arylidene indan-1,3-diones 11-13 re sults in moderate to good yields of the 4-aryl-5-oxo-4H-indeno[1,2-b]p yran-3-carboxylates 14-19. An ynamine nitrile 24, generated in situ, a lso reacts with 12 and 13, furnishing rather lower yields of the adduc ts 20 and 21.