PROCESS FOR THE PREPARATION OF DIHYDROPYRANS

摘要

The invention provides a process for the preparation of 5,6-dihydro-2H-pyran derivatives, wherein an aldehyde of formula I: <IMG> (I) wherein R1 represents an alkyl, cycloalkyl, aralkyl, alkaryl or aryl group having at most 15 carbon atoms and a diene of formula II: <IMG> (II) wherein R2 and R3 represent a hydrogen atom or an alkyl group having 1-6 carbon atoms are reacted in a DielsAlder-type reaction under the influence of an inorganic Lewis acid catalyst, producing a compound of formula III wherein R1-R3 have the meaning given above. <IMG> (III) Preferably R1 represents a 1-6 carbon atom alkyl group, a phenyl group or an o-, m- or p-tolyl group. Isoprene or 2-methyl-1,3-pentadiene is preferably used as the diene. The preferred catalyst is AlCl3 or SnCl4 and an organic nitro compound may be used as the co-catalyst.