Development of Novel Synthetic Reactions Using Cationic Reagents

在路易斯酸的作用下，2,2 -二甲氧基乙基酯很容易原位转化为1,3 -二恶氧兰-2-镓阳离子。因此，通过2,2 -二甲氧基乙基酯与胺在二氯（三氟甲烷磺酸）钛存在下的反应，得到了选择性单保护的不对称1,3 -二酮。2,2 -二甲氧基乙基丙烯酸酯是一种容易通过Mitsunobu反应制备的化合物，在-78℃的温度下，在路易斯酸（IV）氯化钛的存在下，生成相应的Diels-Alder加合物，产率高。此外，由2,2 -二甲氧基乙基2烯酸酯衍生的2-（i -烯基）- 1,3 -二恶唑-2-炔离子与氨基反应，主要生成合成Michael加合物，产率高。这是对α、β -不饱和酯衍生物与烯酸酮等价物的Michael反应具有如此高的同步选择性的第一个例子。已知α -亚砜基参与到邻近的阳离子中心，并研究了利用亚砜基参与的合成方法。在一定量的路易斯酸的催化作用下，缩醛-磺酰基与硅烯醇醚、烯酮-缩醛和烯丙基硅烷等硅基化碳亲核试剂反应顺利，主要通过缩醛-硫原子的不对称诱导生成具有高非对映选择性的抗克拉姆加合物。此外，（α -亚砜基甲基）醋酸烯丙酯在路易斯酸的催化作用下与硅基化碳亲核试剂反应，以中高收率和高区域选择性在亚砜基甲基上生成主要的α -加合物。反应可通过乙磺酸离子中间体进行。

2, 2-Dimethoxyethyl esters are easily transformed into 1, 3-dioxolan-2-ylium cations in situ on the action of Lewis Acid. Thus selectively monoprotected unsymmetrical 1, 3-diketones were obtained by the reaction of 2, 2-dimethoxyethyl esters with enamines in the presence of dichlorobis(trifluoromethanesulfonato)titanium. And 2, 2-dimethoxyethyl acrylate, which is easily prepared by the Mitsunobu reaction, reacts with dieties at -78ﾟC in the presence of a Lewis acid such as titanium(IV)chloride to afford the corresponding Diels-Alder adducts in high yields. Furthermore, 2-(I-alkenyl)-I, 3-dioxolan-2-ylium cations derived from 2, 2-dimethoxyethyl 2alkenoates react with enamities to predominantly give syn Michael adducts in good yields. This is the first example of such a high syn-selectivity for the Michael reaction of alpha, beta-unsaturated ester derivatives with ketone enelate equivalents.An alpha-Sulfenyl group is known to participate to the neighboring cationic center and synthetic methodologies using sulfenyl group participation was also investigated. alpha-Sulfenyl acetals reacted smoothly with silylated carbon nucleophiles such as silyl enol ether, ketene silyl acetal, and allylsilane in the presence of a catalytic amount of Lewis acid mainly to give anti-Cram adducts with high diastereoselectivity by the asymmetric induction of the alpha-sulfur atom of the acetals. As well, (alpha-Sulfenylmethyl)allyl acetates reacted with silylated carbon nucleophiles in the presence of a catalytic amount of a Lewis acid to give mainly alpha-adducts at the sulfenylmethyl group in moderate to good yields with high regioselectivity. The reaction may proceed via episulfonium ion intermediates.