ヌクレオシドの新しい高立体選択的合成法 : 新しいジェノフィルの創製と還元条件下での逆アルドール反応の利用

概要

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New dienophiles, dimethyl acetoxymethylenemalonate, and its analogues such as methyl E- 3- acetoxy2-cyanoacrylate, 2, 4-dioxo-1, 3-oxazine-5-carboxylates, 1, 3-dithiethan-, and 1, 3-dithiolan-2-ylidenemalonate oxides, have been synthesized. These dienophiles readily reacted with cyclopentadiene to give Diels-Alder adducts, whose acetonide derivatives were transformed to carbocyclic C- nucleoside precursors via RRA (reductive retrograde aldol) reaction as a key step. The high pressure mediated Diels-Alder reaction of furan with the same dienophiles also gave the cycloadducts, which on RRA reaction afforded the corresponding Cnucleoside precursors. Essentially the same methodology has also been applied successfully to the synthesis of carbocyclic nucleosides. Use of chiral dienophiles, such as di-l-menthyl acetoxymethylenemalonate, for the above reaction has opened a new route to the enantioselective synthesis of C-nucleosides. The mechanism of asymmetric Diels-Alder reaction is also discussed on the basis of possible conformations of the dienophiles in the presence of suitable catalysts or under high pressure.