Erythro-Selective Aldol Reaction Using Phenyldichloroborane

Hamana, Hiroshi; Sasakura, Kazuyuki; Sugasawa, Tsutomu

doi:10.1246/cl.1984.1729

Cited by 34 publications

(19 citation statements)

References 3 publications

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“…From here, the synthetic route continued in similar fashion to the sequence leading to (+)-irciniastatin A ( 1 ). 9 Aldol union 35 between aldehyde 45 and ketone (+)- 6 pleasingly furnished β-hydroxyketone (+)- 46 in 70% yield, with minor concomitant lactonization (10:1) and excellent diastereoselectivity (>20:1). 36 Chelation-controlled reduction 37 resulted in a mixture of the desired syn diol and the corresponding lactone (ca.…”

Section: Resultsmentioning

confidence: 99%

Total Synthesis of (+)-Irciniastatin A (a.k.a. Psymberin) and (−)-Irciniastatin B

Jurica

Walsh

et al. 2013

J. Org. Chem.

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A unified synthetic strategy to access (+)-irciniastatin A (a.k.a. psymberin) and (−)- irciniastatin B, two cytotoxic secondary metabolites, has been achieved. Highlights of the convergent strategy comprise a boron-mediated aldol union to set the C(15)–C(17) syn-syn triad, reagent control to set the four stereocenters of the tetrahydropyran core, and a late-stage Curtius rearrangement to install the acid-sensitive stereogenic N,O-aminal. Having achieved the total synthesis of (+)-irciniastatin A, we devised an improved synthetic route to the tetrahydropyran core (13 steps) compared to the first-generation synthesis (22 steps). Construction of the structurally similar (−)-irciniastatin B was then achieved via modification of a late-stage (−)-irciniastatin A intermediate to implement a chemoselective deprotection/oxidation sequence to access the requisite oxidation state at C(11) of the tetrahydropyran core. Of particular significance, the unified strategy will permit late-stage diversification for analogue development, designed to explore the biological role of substitution at the C(11) position of these highly potent tumor cell growth inhibitory molecules.

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Section: Resultsmentioning

confidence: 99%

Total Synthesis of (+)-Irciniastatin A (a.k.a. Psymberin) and (−)-Irciniastatin B

Jurica

Walsh

et al. 2013

J. Org. Chem.

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“…was readily prepared by a Paterson boronmediated aldol addition (see section 5.1) between 2-butanone and aldehyde 97, and then underwent epoxide ring opening and methylation to give tetrahydropyran 98. Selective Z enolization of ketone 98 was carried out with Cl 2 BPh and iPr 2 NEt, [50] where addition to aldehyde 99 gave the 1,5-synadduct 100 (90 %, > 20:1 d.r.). A Narasaka reduction [12] then established the all-syn configuration of the three stereocenters at C15-C17 in 1,3-diol 101.…”

Section: Control By Chiral Enolates Through 14-and 15-stereoinductionmentioning

confidence: 99%

The Impact of the Mukaiyama Aldol Reaction in Total Synthesis

2013

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Four decades since Mukaiyama's first reports on the successful application of silicon and boron enolates in directed aldol reactions, the ability of this highly controlled carbon-carbon bond-forming method to simultaneously define stereochemistry, introduce complexity, and construct the carbon skeleton with a characteristic 1,3-oxygenation pattern has made it a powerful tool for natural product synthesis. This Minireview highlights a number of representative total syntheses that demonstrate the impact of the Mukaiyama aldol reaction and discusses the underlying mechanistic rationale that determines the stereochemical outcomes.

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“…But, starting ketone 11 and desilylated starting material ( 13 ) were also isolated. Encouraged by this result, we investigated other boron Lewis acids (Cy 2 BOTf or PhBCl 2 31 ), but these also resulted in very low conversion (Table 1, entry 1). Importantly, these experiments revealed that adding the Lewis acid to a mixture of the substrate and base could minimize desilylation of ketone 11 .…”

Section: Resultsmentioning

confidence: 99%

Torsional steering as friend and foe: development of a synthetic route to the briarane diterpenoid stereotetrad

Moon

Harned

2017

Org. Biomol. Chem.

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Two synthetic routes to the briarane stereotetrad have been investigated. The first route employed a boron aldol reaction to establish the stereogenic all-carbon quaternary carbon (C1). In this case, it was found that torsional steering in the transition state led to the formation of the undesired configuration at this position. The second route makes use of a highly diastereoselective acetylide conjugate addition/β-ketoester alkylation sequence to construct the vicinal C1 and C10 stereocenters with the correct relative configuration. Originally, it was proposed that torsional steering in the transition state for the ketoester alkylation step was the primary factor responsible for generating the major product. DFT calculations reveal that while torsional steering does play a role, larger conformational factors must also be considered. Tthese calculations also reveal that an unusual C–H•••π (alkyne) interaction may contribute to lowering the energy of one transition state that leads to the observed stereoisomer. Ultimately, this strategy leads to a concise synthesis (under 10 steps) of the stereotetrad core common to the briarane diterpenoids.

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Erythro-Selective Aldol Reaction Using Phenyldichloroborane

Abstract: High erythro-selectivity could be attained in the aldol reaction of ethyl ketones with aldehydes using phenyldichloroborane in the presence of ethyldiisopropylamine.

Cited by 34 publications

References 3 publications

Total Synthesis of (+)-Irciniastatin A (a.k.a. Psymberin) and (−)-Irciniastatin B

Total Synthesis of (+)-Irciniastatin A (a.k.a. Psymberin) and (−)-Irciniastatin B

The Impact of the Mukaiyama Aldol Reaction in Total Synthesis

Torsional steering as friend and foe: development of a synthetic route to the briarane diterpenoid stereotetrad

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