Vinyl isobutyl ether → 4-(p-Tert.-butylphenyl)-3-methyl-6-isobutoxy-5,6-dihydropyran

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3,000 g of 3-(4-tert.-butylphenyl)-2-methylprop-2-enal III and 2,000 g of vinyl isobutyl ether IV are introduced into a 10 l stirred autoclave, and 5 g of hydroquinone are added to the reaction mixture for stabilization. The autoclave is closed and then flushed with nitrogen, after which it is heated to 220° C., maintained under these conditions for 18 hours and then let down and opened. The reaction mixture (4,855 g) consists of about 39.6% of the desired product V. When the reaction mixture is worked up by fractionation in a laboratory column containing 10 sieve trays, a total of 1,379 g of the compound V of boiling point 135°-146° C. under 2 mbar are obtained from the 1,923 g shown to be present in the crude mixture by gas chromatographic analysis. This corresponds to a yield of 23%, based on the starting material III employed. 1,745 g of III, which contains some product V, are recovered. The last-mentioned amounts are reused for the reaction with vinyl isobutyl ether.

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