addition product (+)-(3S,4S,5R)-9 possessing a 3,4-cis-dihydroxy-δ-lactone in 78% overall yield from (4S,5R)-4. The obtained (+)-(3S,4S,5R)-9 was subsequently converted to methyl D-digitoxoside (pyranoside) (12) in 13% overall yield and methyl D-digitoxoside (furanoside) (12) in 20% overall yield. The reaction of benzyl-osmundalactone (4R,5S)-3 and MeOH in the presence of Amberlyst A-26 as a basic catalyst
向渗透性内酯(4S,5R)-4中添加4 eq的
氯醛可定量形成
半缩醛衍
生物(4S,5R)-8,将其用
甲烷磺酸处理,得到分子内的Micheal加成产物(+)-(具有3,4-顺式-二羟基-δ-内酯的3S,4S,5R)-9从(4S,5R)-4的总产率为78%。随后将获得的(+)-(3S,4S,5R)-9转化为总产率为13%的甲基D-数字氧苷(
吡喃糖苷)(12)和总产率为20%的甲基D-数字氧苷(
呋喃糖苷)(12) 。在Amberlyst A-26作为碱性催化剂的存在下,苄基-磺基内酯(4R,5S)-3与MeOH的反应得到3,4-trans-δ-内酯(-)-(3S,4R,5S)-20产率为28%,3,4-顺-δ-内酯(-)-(3R,4R,5S)-21产率为45%。(-)-(3S,4R,5S)-20的Dibal-H还原反应,然后进行催化加氢得到L-夹竹桃糖(6),总产率为86%,