Enantioselective synthesis of alpha-tertiary hydroxyaldehydes by palladium-catalyzed asymmetric allylic alkylation of enolates.
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Aldehydes↗
Biomedical subjects
Barry M Trost
Publications and source records attributed to Barry M Trost.
A heterodinuclear asymmetric catalyst for conjugate additions of alpha-hydroxyketones to beta-substituted nitroalkenes.
[Structure: see text] The bis-ProPhenol ligand was designed to facilitate formation of hetereodinuclear complexes based upon the large difference in pKa of the one phenolic OH group to the tertiary OH groups. In exploring the first example of hydroxyacetophenones as donors in asymmetric Michael reactions with nitroalkene acceptors, the best stereocontrol was observed with a zinc/magnesium dinuclear complex where enantiomeric excesses ranged up to 92% for the major anti diastereomer.
Journal Article↗
Asymmetric synthesis of alpha-substituted aldehydes by Pd-catalyzed asymmetric allylic alkylation-alkene isomerization-Claisen rearrangement.
[Structure: see text] Enantiospecific aliphatic Claisen rearrangement was realized with generally high chirality transfer. The requisite substrates were synthesized via Pd-catalyzed asymmetric allylic alkylation (AAA) from easily obtained starting materials. After protection, the resultant bisallyl ethers underwent olefin isomerization and in situ Claisen rearrangement (ICR) to generate alpha-chiral aldehydes. Remarkable chemoselectivity in the olefin isomerization step was observed. An asymmetric synthesis of communiol A was accomplished applying this methodology.
Aldehydes↗
Palladium-catalyzed asymmetric [3 + 2] trimethylenemethane cycloaddition reactions.
Transition-metal-catalyzed trimethylenemethane (TMM) [3 + 2] cycloadditions provide direct routes to functionalized cyclopentanes. This reaction has been shown to be a highly chemo-, regio-, and diastereoselective process. We report a palladium-catalyzed asymmetric [3 + 2] trimethylenemethane (TMM) cycloaddition between 3-acetoxy-2-trimethylsilylmethyl-1-propene and various di- and trisubstituted olefins. Yields of exo-methylenecyclopentane products range from 59 to 99%, and enantiomeric excesses range from 58 to 92% ee.
Catalysis↗
Catalytic enantioselective synthesis of adociacetylene B.
A catalytic enantioselective total synthesis of adociacetylene B (2) in five steps is reported. The efficiency of this synthesis was enabled by an asymmetric zinc alkynylation catalyzed by the proline-derived ligand (1).
Alkynes↗
Palladium-catalyzed DYKAT of butadiene monoepoxide: enantioselective total synthesis of (+)-DMDP, (-)-bulgecinine, and (+)-broussonetine G.
Palladium catalyzed asymmetric allylic alkylation reaction of an amine with two equivalents of butadiene monoxide allows for the expedient synthesis of trans- and cis-2,5-dihydropyrroles. The versatility of these chiral synthons towards the synthesis of a wide variety of iminosugar natural products was demonstrated with the short and high yielding asymmetric syntheses of (+)-DMDP, and (-)-bulgecinine. In addition, the first total synthesis of (+)-broussonetine G, a potent glycosidase inhibitor, is described along with the assignment of its relative and absolute stereochemical configuration.
Alkaloids↗
Ruthenium-catalyzed alkylative lactonization and carbocyclization.
[reaction: see text] The cationic ruthenium complex [CpRu(NCCH3)3]PF6 promotes the coupling of monosubstituted allene carboxylic acids and simple alpha,beta-unsaturated olefins to form five- and six-membered lactones. The mild reaction conditions allow for the presence of various functional groups.
Alkenes↗
Vanadium-catalyzed addition of propargyl alcohols and imines.
A Mannich-type addition of propargylic alcohols and N-methoxycarbonylimines has been achieved by using a vanadium catalyst. The reactivity of the vanadium catalyst could be modulated by modifying the silanol ligands to avoid the background reaction. The strategy described herein provides an atom-economical access to beta-aryl-substituted Z-enones with an allylic amino functional group, which are not readily accessible with other methods.
Alkynes↗
Sequential Ru-Pd catalysis: a two-catalyst one-pot protocol for the synthesis of N- and O-heterocycles.
An atom economic, selective, and highly practical two-metal one-pot synthesis of heterocycles has been developed that efficiently affords enantio- and diastereopure N- and O-heterocyclic products. Furthermore, use of a chiral catalyst in the two-metal procedure allows formation of all possible diastereomers, even those that are traditionally difficult to access via cyclization routes due to thermodynamics. Interestingly, the nature of the enantiodiscriminating event differs between the use of amine versus alcohol nucleophiles. The method also affords heterocyclic products that are synthetically useful intermediates. Through the Z-vinylsilane a variety of stereodefined trisubstituted olefin products can be accessed including several all-carbon motifs. Finally, the utility of these heterocyclic products in total synthesis is demonstrated through concise syntheses of a kainoid intermediate, a constituent of oil of rose, and the ring B portion of bryostatin, a potent chemotherapeutic.
Alkynes↗
Palladium-catalyzed enantioselective C-3 allylation of 3-substituted-1H-indoles using trialkylboranes.
We have developed a new enantioselective C-3 allylation of 3-substituted indoles using allyl alcohol and trialkylboranes. Asymmetric syntheses of 3,3-disubstituted indolines and indolenines in enantiomeric excesses up to 90% have been achieved using the bulky borane 9-BBN-C6H13 as the promoter of the reaction. The dependence of the selectivity on the nature of the borane suggests that the boron reagent has a role beyond promoting ionization of the allyl alcohol. A protocol for oxidation of indolenines to oxindoles has also been developed and led to a formal synthesis of (-)-phenserine.
Alkenes↗
Palladium asymmetric allylic alkylation of prochiral nucleophiles: horsfiline.
[reaction; see text] The asymmetric synthesis of the oxindole alkaloid horsfiline is described. A palladium-catalyzed asymmetric allylic alkylation (AAA) is used to set the spiro(pyrrolidine-oxindole) stereogenic center.
Alkaloids↗
Palladium-catalyzed asymmetric ring expansion of allenylcyclobutanols: an asymmetric Wagner-Meerwein shift.
In this study, we developed a palladium-catalyzed atom economic asymmetric Wagner-Meerwein shift of allenylcyclobutanol substrates. It is an excellent method for creating functionalized cyclopentanones with an alpha-chiral O-tertiary center by ring expansion of allenylcyclobutanols. This reaction was initiated by hydropalladation and afforded excellent enantioselectivity as well as atom economy. This method provides an efficient route toward the synthesis of natural products such as trans-kumausyne's family, spiro ring systems. In addition, we obtained excellent diastereoselectivity and enantioselectivity at the same time by using 3-monosubstituted allenylcyclobutanol.
Alcohols↗
New class of nucleophiles for palladium-catalyzed asymmetric allylic alkylation. Total synthesis of agelastatin A.
New classes of nucleophiles, pyrroles, and N-methoxyamides were developed for Pd-catalyzed AAA reactions. By varying the functional groups at the 2-position of pyrroles, either regioisomer of the piperazinone is available. Using one regioisomer, the total synthesis of (+)-agelastatin A in 10 total steps is accomplished. For this synthesis, a new copper-catalyzed aziridination and an indium-catalyzed oxidative ring opening of a N-tosylaziridine were developed. The feasibility of accessing (-)-agelastatin A from the same enantiomer of the chiral catalyst from the other regioisomeric piperazinone is indicated.
Alkaloids↗
Asymmetric allylic alkylation of cyclic vinylogous esters and thioesters by Pd-catalyzed decarboxylation of enol carbonate and beta-ketoester substrates.
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Alkylation↗
Molybdenum-catalyzed asymmetric allylation of 3-alkyloxindoles: application to the formal total synthesis of (-)-physostigmine.
The first example of Mo-catalyzed asymmetric allylation for the generation of quaternary stereocenters at a prochiral nucleophile is reported. A variety of 3-alkyl oxindoles can be alkylated with high yields and enantioselectivity. This method provides expedited access to (-)-physostigmine and its analogues.
Alkylation↗
Palladium-catalyzed asymmetric allylic alkylation of meso- and dl-1,2-divinylethylene carbonate.
The palladium-catalyzed asymmetric allylic alkylation of a 1:1 mixture of dl- and meso-1,2-divinylethylene carbonate is reported. For the first time, both the ionization and nucleophilic addition steps of the catalytic cycle act as enantiodiscriminating steps to give a single product in high enantiomeric excess. The reactions proceed in >98% ee to efficiently generate useful chiral building blocks from acrolein. The absolute and relative configurations of iso-cladospolide B and 11-epi-iso-cladospolide B were verified by total synthesis, solving an apparent discrepancy in the literature.
Alcohols↗
A direct catalytic asymmetric Mannich-type reaction via a dinuclear zinc catalyst: synthesis of either anti- or syn-alpha-hydroxy-beta-amino ketones.
The use of imines bearing a hydrolyzable nitrogen substituent in direct asymmetric Mannich reactions with alpha-hydroxyketones is developed. Previous work focused on the use of N-arylimines or nonenolizable imines, and the latter with only methoxy-substituted alpha-hydroxyacetophenones. Using a dinuclear catalyst devised from 2,6-di-(S)-2'-diphenylhydroxymethylpyrrolidino-N-methyl)-4-methylphenol and diethylzinc, a broad array of hydroxyacetylated aromatics, including phenyl, 2-furyl, 1-naphthyl, and 2-naphthyl, react well. In addition, the reactions focused on the use of enolizable imines. With the N-diphenylphosphinoyl, the reactions are anti selective with enantiomeric excesses ranging from 83 to 99%, except for the reaction of the 2-methoxy-2'-hydroxyacetylbenzene. With the N-Boc-imines, the reactions were syn selective with enantiomeric excesses from 90 to 94%. The dependence of the diastereoselectivity on the nature of the N-substituent presumably arises from the steric demands of the diphenylphosphinoyl group.
Amino Alcohols↗
S,O-acetals as novel "chiral aldehyde" equivalents.
Palladium-catalyzed asymmetric allylic alkylations (AAA) to form "chiral aldehyde" equivalents were investigated. Alpha-acetoxysulfones were formed in high enantiomeric excess as single regioisomers in AAA reactions of allylic geminal dicarboxylates with sodium benzenesulfinate. The directing ability of this novel functional group was highlighted by a series of dihydroxylations, affording syn diols exclusively anti to the acetoxy sulfone as single diastereomers in excellent yields. This is the first example of an asymmetric dihydroxylation protocol that gives the equivalent of reaction with a simple enal. The synthetic value of this process was exemplified by subsequent transformations of the diols including the development of a one-pot dihydroxylation-deprotective acyl migration protocol to give differentially protected 1,2-diols.
Acetals↗