Production of 3,6-dihydro-2H-pyran-2-carboxylic esters by thermal hetero-Diels-Alder reaction involves heating glyoxylic esters in absence of catalyst and stabilizer before addition, preferably dosed addition, of diene

In the production of 3,6-dihydro-2H-pyran-2-carboxylic esters (I) by thermal hetero-Diels-Alder reaction of dienes (II) with glyoxylic esters (III), reaction is carried out in the absence of catalysts and stabilizers and (III) is present initially and is heated to 90-230 deg C, then (II) is added. In the preparation of 3,6-dihydro-2H-pyran-2-carboxylic esters of formula (I) by thermal hetero-Diels-Alder reaction of dienes of formula (II) with glyoxylic esters of formula HC(O)C(O)OR (III), reaction is carried out in the absence of catalysts and stabilizers and (III) is present initially and is heated to 90-230 deg C, then (II) is added: R , R , R , R = H or linear or branched 1-7 C alkyl; R = linear or branched 1-7 C alkyl or a phenyl or benzyl group, which may have 1-5 substituents selected from 1-4 C alkyl, halogen, nitro, 1-4C alkoxy and 1-4C alkoxycarbonyl; R , R = H or linear or branched 1-3 C alkyl; or R R = -(CH2)n-; n = not 1 or 2. Bereitgestellt wird ein Verfahren zur Herstellung von 3,6-Dihydro-2H-pyran-2-carbonsäureestern über eine thermische Hetero Diels-Alder-Reaktion von 1,3-Dienen mit Glyoxylsäureestern ohne Einsatz von Katalysatoren und Stabilisatoren bei Anwendung einer speziellen Dosiertechnik.