Stereochemically Rich Pentaketides from Bis(isoxazolines): A General Strategy for Efficient Polyketide Synthesis
摘要:
A strategy based on diastereoselective dipolar cycloaddition reaction of nitrile oxides and allylic alcoholates has been applied to the synthesis of bis(isoxazolines) that are precursors to polyketide fragments. These intermediates can be elaborated into protected polyols by chemoselective reductive opening of each isoxazoline sequentially or, alternatively, both simultaneously, potentially providing access to all stereoisomers of this carbon skeleton.
Palladium(II)-Catalyzed Exchange and Isomerization Reactions. 17. Exchange of Chiral Allyl Alcohols with Hydroxide, Methoxide, and Phenyl at High [Cl-]. Stereochemistry of the Wacker Reaction
摘要:
At high [Cl-] (> 2.0 M), PdCl42- catalyzes the exchange of chiral allylic alcohols with hydroxy, methoxy, and phenyl to give chiral allyl-substituted olefins. With unsymmetrical olefins, isomerization occurs along with exchange. The hydroxyl exchange occurs in aqueous solution while the other exchanges are carried out in methanol solution. At low [Cl-] (0.1 M) oxidation to the corresponding beta-hydroxy-, methoxy-, and phenyl-substituted carbonyl compounds occurred. The absolute configurations of the oxidation and exchange products should be the same if the same mode of addition to the Pd(II)-pi-complex is operative. The absolute configurations of the oxidation and exchange products for the phenylation reaction were the same, while for hydroxy and methoxy they were different. This result indicates methanol and water must have different stereochemistries of addition at high and low [Cl-]. Thus, previous studies showing anti hydroxypalladation at high [Cl-] are not valid indicators of the stereochemistry at low [Cl-]. If anti addition occurs at high [Cl-], the addition must be syn at low [Cl-].
Succinoylamino hydroxyethylamino sulfonyl urea derivatives useful as retroviral protease inhibitors
申请人:G.D. Searle & Co.
公开号:US06337398B1
公开(公告)日:2002-01-08
Succinoylamino hydroxyethylamino sulfonyl urea derivatives of the formula:
wherein the substituents are as defined in the specification, are effective as retroviral protease inhibitors, and in particular as inhibitors of HIV protease.
Palladium(II)-catalyzed dicarboxymethylation of chiral allylic alcohols: chirality transfer affording optically active diesters containing three contiguous chiral centers
作者:Othman Hamed、Patrick M. Henry、Daniel P. Becker
DOI:10.1016/j.tetlet.2010.04.105
日期:2010.7
This manuscript describes the extension of Stille’s palladium-catalyzed olefin dicarbonylation reaction to chiralallylicalcohols with chiralitytransfer to afford the corresponding chiralalcohol functionalized with bis-carbomethoxy esters, containing three contiguous chiral centers, in good to excellent diastereoselectivities (78–98%).
High regioselectivity for allylic substitution of the cyclopentenyl picolinate 5 with benzylcopper reagent was attained with ZnBr2, and the finding was applied to the p-BrC6H4CH2 reagent. The cyclopentene moiety in the product was reduced to the cyclopentane, and the p-BrC6H4 was converted to the “Cu”C6H4 for the second allylic substitution with picolinate 8 to furnish the title compound after oxidative
用ZnBr 2获得高苄基选择性地用苄基铜试剂对环戊烯基吡啶甲酸5进行烯丙基取代,并将该发现应用于对-BrC 6 H 4 CH 2试剂。将产物中的环戊烯部分还原为环戊烷,将p -BrC 6 H 4转化为“ Cu” C 6 H 4,用吡啶甲酸8进行第二次烯丙基取代,以氧化裂解所得产物得到标题化合物烯烃部分。
Highly Stereoselective C–C Bond Formation by Rhodium-Catalyzed Tandem Ylide Formation/[2,3]-Sigmatropic Rearrangement between Donor/Acceptor Carbenoids and Chiral Allylic Alcohols
作者:Zhanjie Li、Brendan T. Parr、Huw M. L. Davies
DOI:10.1021/ja303023n
日期:2012.7.4
The tandem ylide formation/[2,3]-sigmatropic rearrangement between donor/acceptor rhodium carbenoids and chiral allyl alcohols is a convergent C-Cbond forming process, which generates two vicinal stereogenic centers. Any of the four possible stereoisomers can be selectively synthesized by appropriate combination of the chiral catalyst Rh(2)(DOSP)(4) and the chiral alcohol.
starting materials suffice for the modular synthesis of all possible polypropionate diastereomers. This general method for the diastereoselective synthesis of syn, anti, and methyl ketone aldol adducts utilizes a powerful MgII -mediated, hydroxy-directed nitrile oxide cycloaddition. The free hydroxy group provides an ideal synthetic handle enabling the rapid assembly of complex polyketide structures