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Chiral aldehydes 4a,b, obtained by the ozonolysis of the corresponding N,N′‐fumaroylbis[(S)‐proline esters] 3 react in the presence of lanthanoid chelate complexes Eu(fod)3 or Eu(hfc)3 with silyloxydienes 7 or 12 to give δ‐lactones 10 or dihydro‐γ‐pyrones 13 with very high diastereomeric ratios (up to 99:1). The absolute configuration of the predominating diastereoisomer of compound 10b was unequivocally determined by X‐ray structural analysis.

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From the corresponding heterocyclic amino acids 2 and 9a the heterocyclic systems imidazo[1,5‐a]pyridine (3) and imidazo[1,5‐a]quinoline (10) are easily accessible. From compound 7 the tricyclic system 11 was prepared and from compound 17a a pyridyl‐1,2,4‐triazinone (18) could be obtained.