Enolic ortho ester
(2S,3S)-2,3-bis(methoxymethyl)-1,4,6-trioxaspiro[4.5]dec-7-ene
(10b) was synthesized in 65% yield by cycloadditon of acrolein with the
ketene acetal
(4S,5S)-4,5-bis(methoxymethyl)-2-methylidene-1,3-dioxolan
(7), derived by potassium t-butoxide treatment of
(4S,5S)-4,5-bis(methoxy-
methyl)-1,3-dioxolan (4). Lewis acid catalysed reaction
(TiCl4, CH2Cl2, –78°) of
the enolic ortho ester (10b) with the ketene silyl acetal
3-phenylmethyl-2-trimethylsilyloxy-4,5-dihydrofuran (15) afforded the formyl
keto ester
3-[4′,5′-bis(methoxymethyl)-2′-(4′′-oxobutyl)-1′,3′-dioxolan-2′-yl]-3-phenylmethyl-4,5-dihydrofuran-2(3H)-one
(16) (39%) with only poor diastereoselectivity.
Attempts to make the bis(phenylmethyl) analogue (10a) of enolic ortho ester
(10b) were thwarted by the finding that the required ketene acetal (9),
analogous to (7), could not be generated by elimination from
(4S,5S)-2-bromomethyl-4,5-bis(phenylmethyl)-1,3-dioxolan
(6), or from the derived phenyl selenoxide (8), under a variety of conditions.
烯醇原酯
(2S,3S)-2,3-bis(methoxymethyl)-1,4,6-trioxaspiro[4.5]dec-7-ene
(10b) 是通过环加成法合成的,收率为 65%。
烯酮缩醛
(4S,5S)-4,5-双(甲氧基甲基)-2-亚甲基-1,3-二氧戊环(7)。
(7),通过叔丁醇钾处理(4S,5S)
(4S,5S)-4,5-bis(methoxy-
甲基)-1,3-二氧戊环(4)。路易斯酸催化反应
(TiCl4,CH2Cl2,-78°)的路易斯酸催化反应。
路易斯酸催化反应(TiCl4,CH2Cl2,-78°),烯醇原酯(10b)与酮烯硅烷基缩醛发生反应
3-苯基甲基-2-三甲基硅氧基-4,5-二氢呋喃(15)发生反应,得到甲酰基
酮酯
3-[4′,5′-双(甲氧基甲基)-2′-(4′′-氧代丁基)-1′,3′-二氧戊环-2′-基]-3-苯甲基-4,5-二氢呋喃-2(3H)-酮
(16) (39%),但非对映选择性较差。
试图制造烯醇原酯(10b)的双(苯基甲基)类似物 (10a)
(10b) 的双苯甲基类似物 (10a) 的尝试受挫,因为发现所需的烯酮缩醛 (9)
与 (7)类似,无法通过从(4S,5S)-(7)中消除生成。
(4S,5S)-2-溴甲基-4,5-双(苯基甲基)-1,3-二氧戊环 (6)
(6) 或衍生的苯基硒氧化物 (8) 在各种条件下都无法生成。