Continuous process for preparing dihydropyrones

A process for preparing a compound of general formula (I),

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• wherein
• R1 is a C1-C8-alkyl, C6-C10-aryl-C1-C4-alkyl or C3-C8-cycloalkyl-C1-C4-alkyl group, and
• R2 is a C1-C8-alkyl group, comprising:
• reacting a) a ketone of formula (II)
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• wherein R1 and R2 are as hereinbefore defined,
• with an acetoacetate in the presence of a strong base and
• b) cyclising the resulting compound of formula (IV)
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• wherein
• R3 denotes a C1-C4-alkyl or benzyl group, by means of a base, wherein a compound of formula II is continuously mixed and reacted with an acetoacetate in the form of its dianion in a microreactor, and subsequently isolating the product compound of the general formula (I).