Opticallyactive 4-hydroxymandelic esters were prepared in good yields and very high diastereoselectivity (up to 96% d.e.) viapara-hydroxyalkylation of phenolic ethers. Enantiomeric pure 4-hydroxymandelic acid is available by hydrolysis.
Total Synthesis of (−)-Heptemerone B and (−)-Guanacastepene E
作者:Aubry K. Miller、Chambers C. Hughes、Joshua J. Kennedy-Smith、Stefan N. Gradl、Dirk Trauner
DOI:10.1021/ja0660507
日期:2006.12.1
stereoselective, and convergent totalsynthesis of the unnatural enantiomer of the neodolastane diterpenoid heptemerone B has been completed. Saponification of (-)-heptemerone afforded (-)-guanacastepene E. The absolute stereochemistry of (-)-heptemerone B was thus established as 5-(S), the same as (-)-guanacastepene E. The longest linear sequence of the synthesis comprises 17 (18) steps from simple
新多拉烷二萜类庚烯酮 B 的非天然对映异构体的简洁、立体选择性和收敛全合成已经完成。(-)-庚烯酮皂化得到(-)-胍那卡司汀E。因此,(-)-庚烯酮B的绝对立体化学确定为5-(S),与(-)-胍那卡司酮E相同。最长的线性序列为该合成包括从简单的已知起始材料开始的 17 (18) 个步骤。我们的一般合成方法整合了一系列不同的反应,包括分子内 Heck 反应以创建一个四元立体中心和一个铜酸盐共轭添加以建立另一个。中央七元环通过不常见的电化学氧化闭合,而五元环通过闭环复分解形成。
Efficient Asymmetric Synthesis of an A‐Ring Synthon for Pd‐Catalyzed Preparation of 1α‐Hydroxyvitamin D Metabolites and Analogs
作者:Julian Loureiro、Lars Kattner、Antonio Mouriño
DOI:10.1002/ejoc.202200314
日期:2022.9.6
An efficient Lewis acid-assisted asymmetric carbonyl-ene reaction to set the 1α-hydroxyl functionality of enol-triflate, precursor of the A-ring of the hormone calcitriol and its 1α-hydroxyderivatives, is described.
描述了一种有效的路易斯酸辅助不对称羰基-烯反应来设置烯醇-三氟甲磺酸酯的 1α-羟基官能团,这是激素骨化三醇及其 1α-羟基衍生物的 A 环的前体。
Stereoselective Synthesis of <i>meso</i>-2,6-Diaminopimelic Acid and Its Selectively Protected Derivatives
作者:Yong Gao、Patricia Lane-Bell、John C. Vederas
DOI:10.1021/jo972133h
日期:1998.4.1
Four synthetic routes to selectively protected derivatives and isomers of meso-diaminopimelic acid (DAP) (1a), a key constituent of bacterial peptidoglycan, were investigated. N-(tert-butyloxycarbonyl)-D-allylglycine (2) and N-(benzyloxycarbonyl)-L-allylglycine (4) were esterified to ethylene glycol and cyclized via olefin metathesis to a protected derivative 7 of 2,7-diaminosuberic acid. Analogous linking of propane-1,3-diol with 2 and potential precursors of N-(benzyloxycarbonyl)-L-vinylglycine moieties, such as N-(benzyloxycarbonyl)-L-glutamate or N-(benzyloxycarbonyl)-L-methionine sulfoxide, gave 12 or 15, both of which produced the alpha,beta-unsaturated ester 14 upon attempted generation of the vinylglycine precursor for olefin metathesis to DAP derivatives. An alternative route, based on SnCl4-catalyzed ene reaction of methyl N-(benzyloxycarbonyl)-L-allylglycinate (18) with glyoxylate esters of phenylcyclohexanol isomers as chiral auxiliaries, gave ca. 85:15 ratios of diastereomeric alcohols (19 or 20). These could be transformed to DAP derivatives in a series of steps employing azide displacement of corresponding mesylates to introduce the second nitrogen. A third method, involving reduction of pure dimethyl (6S)-2-keto-6-[N-(benzyloxycarbonyl)amino]pimelate (32) to the corresponding alcohol 33 with (S)-binaphthol-ruthenium catalyst as the key step, gives a 79:21 isomeric ratio. The fourth route employs the bis(oxazoline)-copper complex 41 as a chiral catalyst for the ene reaction of methyl (S)-4-(phenylthio)allylglycinate (39) and methyl glyoxylate to afford 42 in 94:6 isomeric ratio. Nickel boride removal of sulfur and the double bond in the presence of the Cbz group gives the desired alcohol, dimethyl (2S,6S)-6-[N(benzyloxycarbonyl)amino]-2-hydroxyheptane-1,7-dioate (33). The required selectively protected second nitrogen is introduced using Mitsunobu inversion with N-tert-butyl [[2-(trimethylsilyl)ethyl]sulfonyl]carbamate (34) as a key step.
WHITESELL, J. K.;HWANG-HSING, CHEN;LAWRENCE, R. M., J. ORG. CHEM., 1985, 50, N 23, 4663-4664
作者:WHITESELL, J. K.、HWANG-HSING, CHEN、LAWRENCE, R. M.