Second-Generation Synthesis of the Polypropionate Subunit of Callystatin A Based on Regioselective Internal Alkyne Hydrostannation

Marshall, James A.; Bourbeau, Matthew P.

doi:10.1021/ol026791m

Cited by 37 publications

(11 citation statements)

References 20 publications

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“…Reaction with the primary propargylic acetate 61 followed by iodination gives the alkenyl iodide 62 in 81% overall yield (Scheme 90). 168 A palladium-catalyzed hydrostannation of alkynyl esters 91,169,170 is used in a synthesis of 4-alkylidenebutenolactone 65, a substructure of the carotenoids pyrrhoxanthin and peridinin. It is suggested that in addition to electronic polarization of the acetylenic bond, the presence of the neighboring isopropylidenedioxy group in 63 is responsible for the formation of the single stereo-and constitutional isomer 64 (Scheme 91).…”

Section: Applications To Synthesismentioning

confidence: 99%

Hydrostannation of Alkynes

2019

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In this review, we present an overview of hydrostannation of alkynes until the end of 2018. Mechanism of the tin hydride addition on a triple bond is discussed at the beginning of this review in the presence of metal catalysts as Pd, Ru-based complexes, Lewis acids and under radical conditions. Then, stereoselectivity as well as regioselectivity aspects of tin hydride addition on the carbon triple bond is discussed using metal-catalysis, radical conditions or Lewis acids. In each of these items, the reactions will be studied for terminal alkynes and then, for internal alkynes. Applications of hydrostannation of alkynes using metal-catalysis is presented in a variety of total syntheses with Pd, Mo, Rh and Ru-complexes to provide highly functionalized vinyl stannanes derivatives as key-intermediates. Comparison with other methods providing vinyl stannanes using metallostannation followed by protonation is presented before the last section dealing with a summary of classical experimental conditions used to achieve the hydrostannation of alkynes.

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Section: Applications To Synthesismentioning

confidence: 99%

Hydrostannation of Alkynes

2019

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“…This product was further manipulated to obtain the necessary vinyl iodide 53, which coupled with another segment under Suzuki-coupling conditions to finish (À)callystatin A (Scheme 12). [43] In a similar way, the four stereocenters in the polypropionate marine defense substance (À)-membrenone C were introduced by a sequence involving the addition of chiral allenylmetal reagents to aldehydes, which was followed by a double intramolecular hydrosilylation/oxidation process to install the b-hydroxy ketone subunits, and a double intramolecular aldol reaction to finalize the total synthesis (Scheme 13). [44] Diastereoselective hydroboration of allenylstannane with diisopinocampheylborane [( d Ipc) 2 BH] at À40 to À20 8C followed by a kinetically controlled highly diastereoselective 1,3-boratropic shift afforded chiral allylborane 54.…”

Section: Marshall Et Al Completed the Syntheseis Of Leptostatinsmentioning

confidence: 99%

Allenes in Catalytic Asymmetric Synthesis and Natural Product Syntheses

2012

Angew Chem Int Ed

962

259

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Allenes are the simplest class of cumulenes, with two contiguous C=C bonds, and show unique physical and chemical properties. These features make allenes particularly attractive in modern organic chemistry. In this Review, attention is paid to the advances made in catalytic asymmetric synthesis and natural product syntheses based on well-established reactions of allenes, such as propargylation, addition, cycloaddition, cycloisomerization, cyclization, etc., with or without catalysts. Their versatile reactivity, substituent-loading ability, axial to center chirality transfer, and controllable selectivity allow access to target molecules by unique and efficient approaches. The main topics in this Review are presented with selected examples from 2003 to 2011.

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“…If racemization occurred at the allenyl-Pd intermediate, any product formed would be racemic because racemization must necessarily occur before the transmetalation/reductive elimination step. Therefore, the Pd(II) racemization mechanism remains a possibility with NaOP(O)(OEt) 2 or NaHCO 3 playing the role of LiBr; however, no experimental evidence for this proposal has been gathered. Furthermore, this mechanism seems unlikely due to the weakly nucleophilic character of the phosphate or bicarbonate anions compared to bromide in the reported example.…”

Section: Probing the Stereospecificity Of The Reaction -Optimization mentioning

confidence: 99%

Palladium(0)‐Catalyzed Synthesis of Chiral Ene‐allenes Using Alkenyl Trifluoroborates.

2006

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Enantioenriched allenes serve as chiral transfer reagents, making them attractive synthetic targets. Herein the synthesis of enantioenriched allenes utilizing a Pd(0)-catalyzed cross coupling reaction of propargylic carbonates and -phosphates with alkenyl trifluoroborates is reported. Di-, tri-, and tetrasubstituted allenes were synthesized in moderate to high optical yields. Several racemic allenes possessing various functional groups were also synthesized.

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Second-Generation Synthesis of the Polypropionate Subunit of Callystatin A Based on Regioselective Internal Alkyne Hydrostannation

Abstract: [formula: see text] An improved route to the polypropionate segment of callystatin A is described in which the efficient directed hydrostannation of an internal alkyne and subsequent iodinolysis provides a key vinylic iodide intermediate.

Cited by 37 publications

References 20 publications

Hydrostannation of Alkynes

Hydrostannation of Alkynes

Allenes in Catalytic Asymmetric Synthesis and Natural Product Syntheses

Palladium(0)‐Catalyzed Synthesis of Chiral Ene‐allenes Using Alkenyl Trifluoroborates.

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