Inter- and Intramolecular Diels-Alder Cycloaddition of Enantiopure 4,5-O, C-Functionalized Cyclohex-2-Enone and Its Derivatives Prepared from D-Glucose¹

1. Presented at the XVIIIth International Carbohydrate Symposium, Milan, Italy, July 21-26, 1996.

Abstract

The Lewis acid catalyzed reaction of a D-glucose derived functionalized cyclohex-2-enone 1 with furan provided the 1,4-conjugate adducts 3 and 4. On the other hand, thermal intermolecular Diels-Alder cycloaddition of 1 with 1,3-cyclohexadiene provided two endo-cycloadducts 5 and 6 in a good combined yield. The intramolecular cycloaddition of sorbic acid ester 20 of the allylic alcohol 19, prepared from 1, proceeded under thermal conditions to give a mixture of highly functionalized decalin derivatives 21-23, whose stereostructures were determined by chemical modification.

1. Presented at the XVIIIth International Carbohydrate Symposium, Milan, Italy, July 21-26, 1996.

Notes

1. Presented at the XVIIIth International Carbohydrate Symposium, Milan, Italy, July 21-26, 1996.

A1C1₃ (1.2 eq., CH₂Cl₂, 0 °C 1.5 h) also gave 3 (20%) and 4 (44%), EtAlCl₂ or Et₂AlCl did not give any products.

The following Lewis acids were examined: AlCl₃ (toluene, 40 °C, 5 days); Et₂AlCl (CH₂Cl₂, -78 °C to rt, 1 day); ZnCl₂ (CH₂Cl₂, -15 °C to rt, 1 day); BF₃OEt₂ (CH₂Cl₂, -15°C to rt, 4 h); TMSOTf (CH₂Cl₂, -15°C to rt, 3 h).

When each 5 or 6 was independently subjected to the thermal conditions (200 °C, 1 day), no interconversion was observed. These results indicated that thermal retro-Diels-Alder process did not occur under the conditions used.

Although a trace amount of the diastereomeric β-allylic alcohol could not separated at this stage, this minor component was cleanly removed after the mixture was converted into their tert-butyldimethylsilyl ethers. The major α-silylated product was obtained in 87% yield from 1. The minor β-silyl ether was obtained in 1% yield, and a mixture of them (10%) was also obtained. From these results, we estimated that the diastereoselectivity of the Luche reduction of 1 is more than 8 to 1. Desilylation of the α-silyl ether provided the diastereomerically homogeneous allylic alcohol 19, which was identical with our previously reported sample,⁴ in all respects.

Prolonging the reaction time for completion of the Diels-Alder cycloaddition of the subtrate 20 caused partial decomposition of 20, and the combined yield of 21—23 reduced significantly.