Synthesis of recyclable fluorous chiral ligands and evaluation of their catalytic activity toward asymmetric addition of dimethylzinc to aldehydes.
The asymmetric addition of Me(2)Zn to aldehydes is very slow and mostly gives low ee values. Previously, we reported the synthesis of a fluorous chiral ligand, (4R,5S,alpha'R)-2,2-dimethyl-alpha,alpha,alpha'-tris(perfluorooctyl)-2,3-dioxolane-4,5-dimethanol (1 a), derived from tartarate as a chiral pool. Ligand 1 a showed high activity toward the addition of Me(2)Zn to aldehydes with high enantiomeric excess. However, the very high content of fluorine makes 1 a difficult to dissolve in common solvents; hence, much solvent is required, which limits its use. This report describes the modification of 1 a by replacing either the perfluorooctyl groups with shorter perfluoroalkyl ones or the acetone ketal part with cyclohexanone ketal. The perfluorobutyl analogue 1 c is much more soluble than 1 a and shows comparable asymmetric induction toward the addition of Me(2)Zn to aldehydes. Furthermore, 1 c has a much lower molecular weight than 1 a. This means that 1 c is used in smaller amounts (weight) than 1 a. The cyclohexanone ketal analogue 1 d is more soluble than 1 a and more easily synthesized owing to its high solubility and ease of crystallization. Ligand 1 d showed much higher asymmetric induction toward cyclohexanecarbaldehyde, a branched aldehyde, than 1 a. Thus, 1 a was modified into ligands with higher performance.
Sokeirik
Yasser S
YS
Faculty of Pharmaceutical Sciences, Setsunan University, 45-1 Nagaotoge-cho, Hirakata, Japan.
Hoshina
Akiko
A
Omote
Masaaki
M
Sato
Kazuyuki
K
Tarui
Atsushi
A
Kumadaki
Itsumaro
I
Ando
Akira
A
D000447:Aldehydes / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D004148:Dioxolanes / Q000737:chemistry; D005461:Fluorine / Q000737:chemistry*; D005466:Fluorocarbons / Q000737:chemistry; D008024:Ligands; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
C533059:(4R,5S,alpha'R)-2,2-dimethyl-alpha,alpha,alpha'-tris(perfluorooctyl)-2,3-dioxolane-4,5-dimethanol; D000447:Aldehydes; D004148:Dioxolanes; D005466:Fluorocarbons; D008024:Ligands; D009942:Organometallic Compounds; D005461:Fluorine; C511262:dimethylzinc