Some reactions of 4-methyl-5,6-dihydropyran and its isomers

Conclusions

• 1. 4-Methyl-5,6-dihydropyran is quantitatively hydrogenated in the presence of Pd and Ni-Cr catalysts. Under ionic hydrogenation conditions, the yield of 4-methyltetrahydropyran does not exceed 65%.

• 2. In the reaction between 4-methyl-5,6-dihydropyran and CH₂O in AcOH, the acetates of the isomeric dihydropyranols and pyrandiol diacetate are formed, which on saponification give the corresponding alcohols and 3-hydroxymethyl-4-methyl-4-hydroxytetrahydropyran. This diol can also be obtained by the action of Na in MeOH on the product of acetolysis of cis-10-methyl-1,3,7-trioxadecalin. These reactions are highly stereospecific.

• 3. By the action of monoperphthalic and perbenzoic acids, 4-methyl-5,6-dihydro- and 4-methylenetetrahydropyrans form the corresponding epoxides. In the case of 2-methyl-5,6-di-hydropyran, a mixture of epimers is obtained with the trans-isomer predominating. The hydroperoxide oxidation in the presence of Mo(CO)₆ is accompanied by cleavage of theα-oxide ring.

• 4. The reaction of the epoxides obtained with several secondary amines proceeds with a trans-diaxial cleavage of the oxide ring at the least substituted carbon atom, and the initially formed aminopyranols undergo a complete inversion.