one-step synthesis of allene-1,3-dicarboxylates from acetone-1,3-dicarboxylates in high yields was developed by the use of DMC as a dehydrating reagent. This process opened a new expeditious route to a 1-azabicyclo[3.3.0]octane skeleton of pyrrolizidinealkaloidsfrom dimethyl acetone-1,3-dicarboxylate and bis(2-chloroethyl)amine via a Michael addition and a novel tandem cyclization.
precursors of nitrogen-bridged bicyclic β-enaminoesters . The compounds are prepared either by intramolecular alkylation of β-enaminoesters or by thermolysis of β-enaminoesters . A stereospecific reduction of compounds under thermal control leads to bicyclic β-aminoesters , , or which are good precursors of natural aminoalcohols like lupinine or isoretronecanol .
A new method for the synthesis of the bicyclic enaminoesters b-d by flash vacuum pyrolysis of the Meldrum's acid derivatives b-d is described in which the key step is an intramolecular cyclization of the aminomethyleneketenes b-d.