As a model study on the synthesis of natural products possessing an eight-membered cyclic ether or amine framework such as laurencin (1) and FR900482 (6), two kinds of 2-benzyl oxacyclooctanones (7 and 8) and 2-methyl azacyclooctanones (9 and 10) were synthesized from the corresponding twelve-membered lactam sulfoxides (49-52) by applying our general method for medium-ring ketone synthesis. The corresponding lactam sulfides were readily prepared from the linear ω-tosyl carboxylic acids containing on oxygen atom (11 and 12) or methylcarbamate group (13 and 14) by condensation with 2-cyanoethyl 2-N-methylaminophenyl sulfide followed by alkylation.
Studies on taxane synthesis. I. Synthesis of 3,8,11,11-tetramethyl-4-oxobicyclo[5.3.1]undecane as a model for taxane synthesis.
作者:YASUO OHTSUKA、TAKESHI OISHI
DOI:10.1248/cpb.36.4711
日期:——
The bicyclo [5.3.1] undecanone 5 corresponding to the A and B rings in taxane diterpenes was synthesized from β-ionone.Reduction of the tosylhydrazone 11 with catecholborane afforded the trisubstituted olefin 12 having trans substituents at the C-1 and C-7 positions.The requisite cis-arrangement of these substituents for eight-membered ring formation was induced by epimerization of the aldehyde 13 to give the bicyclic hemiacetal 14.The lithium diisopropylamide-promoted intramolecular cyclization of the twelve-membered lactam sulfoxide 32 proceeded quite smoothly, affording the eight-membered keto sulfoxide 33 in quantitative yield.
Studies on Taxane Synthesis. III. Stereocontrolled Synthesis of a Twelve-Membered Lactam Sulfide as a Precursor of 4,8,11,11-Tetramethyl-3-oxobicyclo(5.3.1)undec-8-ene.
作者:Yasuo OHTSUKA、Takeshi OISHI
DOI:10.1248/cpb.39.1359
日期:——
Stereocontrolled synthesis of two twelve-membered lactam sulfides 37 and 38 as precurors of 8, 11, 11-trimethyl-3-oxobicyclo[5.3.1]undec-8-enes constituting the A and B rins of taxane-diterpenes was achieved.The keystep involves a Diels-Alder reaction of maleic anhydride and the E-diene 18 for introduction of the requisite cis arrangement of substitutions at the C-1 and C-7 positions.The resulting adduct was converted exclusively into the lactone 21b in five steps : 1) hydrolysis, 2) iodo-lactonization, 3) BH3 reduction, 4) Zn reduction, 5) methylation.The benzyl group of 26 could be selectively removed by heating with Raney Ni(W-2) in EtOH in nearly quantitative yield without hydrogenation of the double bond.
A synthesis of the taxane ring system is described. The A-ring moiety 5, containing the carbons for construction of the B-ring, was prepared from Wieland-Miescher ketone via Beckmann fragmentation of the oxime 10. The B-ring was formed by means of 12-membered lactam-sulfoxide ring contraction. The formation of the C-ring was carried out by aldol condensation of the resulting AB-ring moiety 3 followed by intramolecular pinacol coupling to give the tricyclic diol 23.
本文介绍了一种紫杉烷环系统的合成方法。A 环分子 5 含有用于构建 B 环的碳原子,由 Wieland-Miescher 酮通过肟 10 的贝克曼破碎法制备而成。B 环是通过 12 元内酰胺-亚砜环收缩形成的。C 环的形成是通过 AB 环分子 3 的醛醇缩合,然后通过分子内频哪醇偶联得到三环二醇 23。
Studies on taxane synthesis. II. Syntheses of 3,8,11,11-tetramethyl-4-oxo- and 4,8,11,11-tetramethyl-3-oxo-bicyclo[5.3.1]undec-8-enes corresponding to the A- and B-rings of taxane diterpenes.
作者:YASUO OHTSUKA、TAKESHI OISHI
DOI:10.1248/cpb.36.4722
日期:——
Two types of tetramethylbicyclo [5.3.1] undec-8-enes 2 and 3 were synthesized from oc-ionone as a model for taxane synthesis.Introduction of the requisite cis-arrangement of substituents at the C-1 and C-7 positions was carried out by catalytic hydrogenation of the α, β-unsaturated ketone 12. Treatment of the hydroxy ester 27 and 16 with diethyl azodicarboxylate and triphenylphosphine led to regioselective dehydration giving 33 and 43, respectively.Intramolecular cyclization of 41 and 49 with lithium diisopropylamide followed by reductive desulfurization with Na-Hg produced the eight-membered ring ketones 2 and 3, respectively, in good yields.