Preparation of 3,6-dihydro-2H-pyran-2-carboxylic esters

Process for preparing 3,6-dihydro-2H-pyran-2-carboxylic esters of the general formula (I)

• 4
• where
• R1, R2, R3 and R4 are the same or different and are each H or a straight-chain or branched C1-C7-alkyl radical,
• R5 is a straight-chain or branched C1-C7-alkyl radical, a phenyl radical or a benzyl radical,
• R6 and R7 are the same or different and are each H or straight-chain or branched C1-C3-alkyl or together form a —(CH2)n-alkylene radical where n=1 or 2,
• via a thermal hetero Diels-Alder reaction of 1,3-dienes of the general formula (II)
• 5
• where
• R1, R2, R3, R4, R6 and R7 are each as defined for the general formula (I) with compounds of the general formula (III)
• 6
• where
• R5 is as defined for the general formula (I), comprising conducting the reaction in the absence of catalysts and stabilizers by initially charging the compound of the general formula (III) and heating the charge to a temperature of 90-230° C. and adding the 1,3-diene of the general formula (II).