以高非对映异构体比[95:3]获得了外消旋合成结构单元(2 R *,3 R *)-3-甲基-4-(苯硫基)丁丹-2-醇(2 R *,3 R *)- 2。 5,(2 R *,3 R *)/(2 R *,3 S *)-比率是由路易斯酸催化的二甲基锌加成外消旋的2-甲基-3-(苯基硫烷基)丙醛(rac - 1)。由Chirazyme L-2(固定化南极假丝酵母脂肪酶B,CAL-B)催化的醋酸乙烯酯连续两次酰化反应导致四种立体异构体中的三种被优先酯化(2 S,3 S)98:2 dr和98%ee的)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 S,3 S)-2。在第一个CAL-B催化的酰化步骤中获得的(2 R,3 R)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 R,3 R)-2的立体异构不纯乙酸盐为使用CAL-A(固定的Novozyme SP 525)作为催化剂进行水解和再酯化,留下(2 R,3
以高非对映异构体比[95:3]获得了外消旋合成结构单元(2 R *,3 R *)-3-甲基-4-(苯硫基)丁丹-2-醇(2 R *,3 R *)- 2。 5,(2 R *,3 R *)/(2 R *,3 S *)-比率是由路易斯酸催化的二甲基锌加成外消旋的2-甲基-3-(苯基硫烷基)丙醛(rac - 1)。由Chirazyme L-2(固定化南极假丝酵母脂肪酶B,CAL-B)催化的醋酸乙烯酯连续两次酰化反应导致四种立体异构体中的三种被优先酯化(2 S,3 S)98:2 dr和98%ee的)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 S,3 S)-2。在第一个CAL-B催化的酰化步骤中获得的(2 R,3 R)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 R,3 R)-2的立体异构不纯乙酸盐为使用CAL-A(固定的Novozyme SP 525)作为催化剂进行水解和再酯化,留下(2 R,3
Total Synthesis of Brevetoxin A: Part 1: First Generation Strategy and Construction of BCD Ring System
作者:K. C. Nicolaou、Mark E. Bunnage、Daniel G. McGarry、Shuhao Shi、Patricia K. Somers、Paul A. Wallace、Xin-Jie Chu、Konstantinos A. Agrios、Janet L. Gunzner、Zhen Yang
Discussed herein is our first generation strategy for the total synthesis of brevetoxin A. This approach relies upon dissection of the molecule at the nine-membered ring site (ring E), A Wittig coupling of requisite polycyclic fragments 3 and 4 followed by hydroxy dithioketal cyclization was expected to furnish the polycyclic framework of brevetoxin A (1). Intermediate 8 was anticipated to be a valid synthetic precursor to phosphonium salt 3, and its synthesis was accomplished by a bis(lactonization)/thionolactone formation/functionalization sequence. In order to test our synthetic strategy, the synthesis of an advanced model system (36) was attempted. Aldehyde 38 and phosphonium salt 37 were successfully synthesized and coupled through a:Wittig reaction. Unfortunately, the planned hydroxy dithioketal cyclization to form the crucial nonacene (ring E) did not proceed as anticipated and this synthetic approach was discontinued.
Enantiopure building blocks for the synthesis of 3-methyl-2-alkanols. Diastereoselective methylmetal addition to a chiral 2-methylaldehyde followed by lipase catalysed esterification
which left (2R,3R)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2R,3R)-2 of 98:2 dr and 99% ee as the remaining substrate. The individual enantiomers of 2-methyl-3-(phenylsulfanyl)propanal 1 were prepared from readily available (S)- and (R)-3-hydroxy-2-methylpropanoic acid methyl ester and reacted with dimethylzinc to give both enantiomers of (2R*,3R*)-3-methyl-4-(phenylsulfanyl)butan-2-ol (2R, 3R)- or (2S
以高非对映异构体比[95:3]获得了外消旋合成结构单元(2 R *,3 R *)-3-甲基-4-(苯硫基)丁丹-2-醇(2 R *,3 R *)- 2。 5,(2 R *,3 R *)/(2 R *,3 S *)-比率是由路易斯酸催化的二甲基锌加成外消旋的2-甲基-3-(苯基硫烷基)丙醛(rac - 1)。由Chirazyme L-2(固定化南极假丝酵母脂肪酶B,CAL-B)催化的醋酸乙烯酯连续两次酰化反应导致四种立体异构体中的三种被优先酯化(2 S,3 S)98:2 dr和98%ee的)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 S,3 S)-2。在第一个CAL-B催化的酰化步骤中获得的(2 R,3 R)-3-甲基-4-(苯基硫烷基)丁-2-醇(2 R,3 R)-2的立体异构不纯乙酸盐为使用CAL-A(固定的Novozyme SP 525)作为催化剂进行水解和再酯化,留下(2 R,3