| 摘要 |
3,4-dihydro-2H-pyrans I <IMAGE> I where R1, R2, R3 and R4 are each H or C1-C6-alkyl and R3 is not C2-C4-alkyl when A is COOR5+L, and A is COOR5, =CHOR5, in which R5 is C1-C4-alkyl, or CH2OR6, in which R6 is C1-C4-alkyl or is benzyl which is unsubstituted or substituted by C1-C4-alkyl, alkoxy or halogen, or is formyl, C2-C4-alkylcarbonyl or benzoyl which is unsubstituted or substituted by C1-C4-alkyl, alkoxy or halogen, are prepared by eliminating an alcohol from a 2-alkoxytetrahydropyran II <IMAGE> II where R7 is C1-C18-alkyl and A' is COOR5, CH(OR5)2 or CH2OR6, in which R5 and R6 have the meanings stated for I, the elimination being carried out by passing II, in the liquid or gaseous state, into a high boiling mineral oil at above the boiling point of the resulting dihydropyran I, removing I in gaseous form, replenishisng the high boiling mineral oil when it becomes enriched with byproducts, and removing the said mineral oil enriched with byproducts.
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