Tetrahydropyrans and Dihydropyrans

Six-membered Rings. -Tetrahydropyrans and Dihydropyrans Little new work has appeared this year on general methods for the synthesis of tetrahydropyrans. However, Winstead et al. have provided an explanation for the Stapp synthesis of tetrahydropyrans, and in so 

The hetero-Diels-Alder reaction of aldehydes as the 2 component has been extensively studied of late, and this year the use of high pressure both on its own and in combination with Lewis-acid catalysis has been extended. A combination of [Eutfod) ] and high pressure (10 kbar) has been used to prepare amino 

There have been relatively few examples of the hetero-Diels-Alder reaction where the carbonyl group is part of the 4 tt component. This is mainly due to the instability of both starting materials and products to heat and acid, and consequently Lewis-acid catalysis has been of minor applicability. Yamamoto et al. have now shown, however, that the molybdenum complex [Mo02(acac)2] catalyses the 

The application of the hetero-Diels-Alder reaction to natural product synthesis has been reviewed.  

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The oxidation of tetrahydrofuran, tetrahydropyran and dihydropyran produced y-butyrolactone and 5-valerolactone in fairly good yields. Linear ethers, conversely, produced exclusively the corresponding acids, presumably through the in situ hydrolysis of intermediate esters [116]. 

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