Acyclic diastereoselective synthesis using tartrate ester-modified crotylboronates. Double asymmetric reactions with .alpha.-methyl chiral aldehydes and synthesis of the C(19)-C(29) segment of rifamycin S

Roush, William; Palkowitz, Alan D.; Ando, Kaori

doi:10.1021/ja00173a024

Cited by 289 publications

(130 citation statements)

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“…The Ti IV /Schiff base catalyzed vinylogous aldol reaction of dienolate 25. [16] The high selectivity and wide substrate scope of this method makes it useful in complex-molecule total synthesis, as illustrated by the synthesis of macrolactin A [26] and dihydroxy vitamin D 3 . [27] In the synthesis of macrolactin A, both enantiomeric forms of the titanium(iv)-Schiff base complex are employed to construct hydroxy-bearing stereocenters present in two key subunits of the molecule (Scheme 13).…”

Section: Synthetic Equivalents Of Acetoacetate Ester Dianionsmentioning

confidence: 99%

Catalytic, Enantioselective, Vinylogous Aldol Reactions

Denmark¹,

Heemstra²,

Beutner³

2005

Angew Chem Int Ed

447

149

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In 1935, R. C. Fuson formulated the principle of vinylogy to explain how the influence of a functional group may be felt at a distant point in the molecule when this position is connected by conjugated double-bond linkages to the group. In polar reactions, this concept allows the extension of the electrophilic or nucleophilic character of a functional group through the pi system of a carbon-carbon double bond. This vinylogous extension has been applied to the aldol reaction by employing "extended" dienol ethers derived from gamma-enolizable alpha,beta-unsaturated carbonyl compounds. Since 1994, several methods for the catalytic, enantioselective, vinylogous aldol reaction have appeared, with which varying degrees of regio- (site), enantio-, and diastereoselectivity can be attained. In this Review, the current scope and limitations of this transformation, as well as its application in natural product synthesis, are discussed.

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Section: Synthetic Equivalents Of Acetoacetate Ester Dianionsmentioning

confidence: 99%

Catalytic, Enantioselective, Vinylogous Aldol Reactions

Denmark¹,

Heemstra²,

Beutner³

2005

Angew Chem Int Ed

447

149

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“…The control of enantio-and diastereoselectivity is applicable to the synthesis of cis-and trans-2,5-disubstituted dihydrofurans and cis-and trans-2,6-disubstituted dihydropyrans [28,29] with control of absolute and relative stereochemistry with readily available, enantioenriched allylic [30,31] and homoallylic alcohols [32,33] (Scheme 2). For example, 1 a and 1 e reacted with alkoxides derived from (R)-1-octen-3-ol and (S)-4-penten-2-ol, respectively, in the presence of catalysts derived from the two enantiomers of L 2 to form the branched allylic ethers 5, 5' and 6, 6' with excellent yields and regio-and diastereoselectivities.…”

Section: Angewandte Chemiementioning

confidence: 99%

Iridium‐Catalyzed Intermolecular Allylic Etherification with Aliphatic Alkoxides: Asymmetric Synthesis of Dihydropyrans and Dihydrofurans

2004

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Elimination and racemization limit the synthesis of sterically hindered ethers, [1] such as a-chiral ethers, by the Willamson synthesis. Enantioselective transition-metal-catalyzed allylic substitution [2][3][4][5][6] could be used to prepare these materials from achiral or racemic allylic electrophiles, but intermolecular enantioselective reactions of allylic acetates or carbonates with alkoxides are limited. Enantioselective reactions of phenoxides are well documented, [7][8][9] but no metal catalyzes intermolecular enantioselective allylations of alkoxides with broad scope. [10][11][12][13] Lee and Kim [14] as well as Evans and Leahy [15] demonstrated that zinc and copper alkoxides were more reactive for allylic substitution with achiral palladium and rhodium catalysts than alkali metal alkoxides. The palladium-catalyzed reactions generated achiral ethers, but the rhodium-catalyzed reactions formed branched chiral ethers. Reactions of primary alkoxides with optically active allylic acetates occurred with predominant retention of configuration, but reactions of secondary and tertiary alkoxides were conducted with racemic allylic electrophiles. Because the products from reactions of primary alkoxides can be formed by alkylation of an optically active alcohol, but products from reactions of secondary alkoxides cannot, a catalyst that forms optically active products from hindered alkoxides and allylic carbonates is synthetically valuable. We report herein enantioselective reactions of primary, secondary, and tertiary alkoxides with achiral allylic carbonates to form branched chiral allylic ethers in high yields and with high stereoselectivity in the presence of an iridium catalyst containing a phosphoramidite ligand (Scheme 1). [16][17][18][19][20][21][22] To optimize the conditions for the allylation of aliphatic alkoxides with iridium-phosphoramidite catalysts, we studied the reactions of cinnamyl carbonate with benzyloxides (Table 1). Careful selection of carbonate, alkoxide counterion, and nitrogen substituents in the ligand was essential for high yields. Cinnamyl carbonates with small alkyl groups underwent transesterification in competition with etherification, but tert-butyl cinnamyl carbonate (1 a) provided the

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“…The synthesis began with Roush crotylboration [25] of a well-known aldehyde 7 [26] to give alcohol 9 in 93% yield and a diastereoselection of 91:9 (Scheme 2). Treatment of alcohol 9 with KHMDS and BnBr furnished the requisite benzyl ether 10.…”

Section: +mentioning

confidence: 99%

Eight‐Step Synthesis of Routiennocin

Matsumoto¹,

Kozmin²

2008

Adv Synth Catal

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Routiennocin is a member of a family of polycyclic pyrrole ether antibiotics that simultaneously uncouple oxidative phosphorylation and inhibit ATPase as a result of selective complexation of divalent metal ions. We describe a concise synthesis of routiennocin with the longest linear sequence of 8 steps. Our synthesis features a unique bi-directional strategy, which entails a sequential ring-opening/cross metathesis of a highly strained cyclopropenone acetal. This approach enables rapid and highly convergent assembly of the fully extended polyketide subunit of this natural product from readily available homoallylic alcohol precursors.

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Acyclic diastereoselective synthesis using tartrate ester-modified crotylboronates. Double asymmetric reactions with .alpha.-methyl chiral aldehydes and synthesis of the C(19)-C(29) segment of rifamycin S

Cited by 289 publications

References 0 publications

Catalytic, Enantioselective, Vinylogous Aldol Reactions

Catalytic, Enantioselective, Vinylogous Aldol Reactions

Iridium‐Catalyzed Intermolecular Allylic Etherification with Aliphatic Alkoxides: Asymmetric Synthesis of Dihydropyrans and Dihydrofurans

Eight‐Step Synthesis of Routiennocin

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