Acetals, acid catalyzed from Grignard reagents

The S-ifl type compounds 72, prepared from the reaction of MBH acetates and Grignard reagents, have been treated with 3 equiv. of H2SO4 at 60-70 °C, giving 3,4-dihydronaphthalenes 74 in moderate yields via an acid-catalyzed Friedel-Crafts-type reaction and subsequent acid hydrolysis of the ester moiety (Scheme 4.24). However, when the reactions were conducted at reduced temperature (0-10 °Q, 5,5-dimethyllactone derivatives 73 were obtained in 70-76% yields via acid-catalyzed lactonization. Such lactones could also be transformed into 3,4-dihydronaphthalenes 74 by treatment with H2SO4 in benzene at elevated temperature (60-70 °Q. 

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