The [4+2] cycloaddition reaction of diethyl ketomalonate and butyl glyoxalate with unactivatcd 2-aza-1,3-dienes 1 is described for the first time. The inability of the carbon dioxide to undergo [4+2] cycloaddition reactions with dienes is well known.t An alternative procedure is the use of diethylketomalonate as dienophile, because the diester groups attached to the carbonyl can be readily transformed in the carbonoxygen double bond,2 Moreover, the two diester groups are very effective in the polarization of the carbonyl in the Diels-Alder reaction with dienes.3 In all previously reported cycloaddition reactions with diethylketomalonate only carbon dienes were employed.2T3 in this paper, we report the first example of a Diels-Alder reaction of unactivated 2-aza-1,3-dienes 1 with diethylketomalonate. In previous papers,4 we have indicated the participation of unactivated 2-aza-1,3-dienes 1 in [4+2] cycloadditions with different heterodienophiles.
The reaction of 1 (10 mmol) with diethylketomalonate (10 mmol) (dry THF, 80% 14 -20 h), gave only the Diels-Alder adduct 2 when the solvents were removed (Scheme I, Table I).