P-20 アシルニトロソ化合物の分子内ヘテロDiels-Alder反応を活用するアルカロイドのキラル合成(ポスター発表の部)

抄録

In an aqueous media, intramolecular hetero Diels-Alder cycloadditions of the chiral acylnitroso compounds 15a-d and 19a, b, generated from the chiral hydroxamic acids 14a-d and 18a, b, respectively, by in situ periodate oxidation, shows a pronounced enhancement (1.3-1.9:1 to 4.1-5.0:1) of the trans selectivity (with respect to C-4a and C-5) leading to the trans- 1,2-oxazinolactams 16a-d and 20a, b, compared with the results obtained by employing nonaqueous conditions. The trans stereoselectivity enhancement observed in these aqueous intramolecular cycloadditions would be explained by considering the hydrophobic packing effect which may have served to stabilize the more compact boat-like conformer 22A, leading to the trans adducts 16a-d and 20a, b, rather than the chair-like conformer 22B leading to the cis adducts 17a-d and 21a, b. The trans-1,2-oxazinolactams 16a, b and 20a thus obtained via these reactions were utilized as chiral precursors to synthesize optically active natural alkaloids including (-)-indolizidines [205A (7), 207A (8), 209 B (9), and 235B (10)] and (-)-pumiliotoxin C (11) both as poison-dart alkaloids, (-)-nupharamine (12), and (-)-swainsonine (13) in enantiocontrolled manner.