Cycloaddition Across the Benzofuran Ring as an Approach to the Morphine Alkaloids.

[摘要]：The intramol. Diels-Alder reaction of several amidofurans tethered onto a benzofuran ring was examd. as a strategy for the synthesis of morphine. Bromo substitution on the furan ring did not provide sufficient activation to allow the cycloaddn. to take place across the arom. benzofuran. However, the presence of a large o-methylbenzyl group on the amido nitrogen atom causes the reactive s-trans conformation of the amidofuran to be highly populated, thereby facilitating its Diels-Alder cycloaddn. across a tethered benzofuran to form the I.

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