Effects of Olefin Geometry on the Stereochemistry of Lewis Acid Mediated Additions of Crotylstannanes to Aldehydes

Keck, Gary E.; Savin, Kenneth A.; Cressman, Erik N.K.; Abbott, Duane E.

doi:10.1021/jo00104a054

Cited by 108 publications

(79 citation statements)

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“…The high selectivity of this reaction is attributed to the matched facial selectivity of the chiral allylsilane and the (2R, 4R, 5S)-enantiomer of the SnCl 4 -chelated chiral aldehyde in the favored syn-synclinal transition state 16. 6,16,20 Woerpel and coworkers have previously described a kinetic resolution in a double asymmetric [3+2] annulation reaction of a racemic allylsilane and a chiral auxiliary-bearing α-keto ester to prepare highly-substituted tetrahydrofurans as single enantiomers. 21 Our methodology is complementary in that it takes advantage of the stereochemistry inherent in the annulation substrates.…”

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confidence: 99%

Synthesis of (+)-Bullatacin via the Highly Diastereoselective [3+2] Annulation Reaction of a Racemic Aldehyde and a Nonracemic Allylsilane

et al. 2005

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A total synthesis of (+)-bullatacin has been accomplished via a diastereoselective [3+2] annulation reaction of the highly enantiomerically enriched allylsilane 3 and racemic aldehyde 4, which provides the key bis-tetrahydrofuran fragment 15 with ≥ 20 : 1 ds.(+)-Bullatacin (1) is one of more than 350 Annonaceous acetogenins isolated from the tropical plant family Annonaceae (Figure 1). Many members of this structurally diverse family of natural products exhibit impressive antitumor activity in human tumor cell lines. 1 The acetogenins contain a long aliphatic backbone bearing a terminal butenolide unit and one or more tetrahydrofuran rings and hydroxyl groups at internal positions of the aliphatic chain. These compounds are intriguing synthetic targets owing to the variation of stereochemistry around the tetrahydrofuran rings and at the sites bearing additional hydroxyl groups. 2, 3The [3+2]-annulation reaction of aldehydes and chiral allylsilanes is an important method for the stereocontrolled synthesis of substituted tetrahydrofurans. 4, 5 β-Silyloxy-substituted allylsilanes undergo [3+2] annulation reactions with aldehydes and certain electrophilic ketones to give either 2, 5-trans or 2, 5-cis substituted tetrahydrofurans with excellent selectivity, depending on the use of chelating or non-chelating Lewis acids, respectively. 6 We have recently utilized this methodology in a highly stereoselective total synthesis of asimicin (2). 7As part of ongoing studies focusing on the development of a stereochemically general synthesis of members of the acetogenin family, we have developed and report herein a highly stereoselective synthesis of bullatacin (1), 8 which differs from asimicin (2) at a single stereocenter (C-24). We envisaged that the bis-tetrahydrofuran core unit of bullatacin could be synthesized from sequential chelate-controlled [3+2] annulation reactions of allylsilanes 3 and 6 (Figure 2). The proposed [3+2] annulation of 3 and 4 is expected to be a stereochemically matched double asymmetric reaction under chelate-controlled conditions, by analogy with the corresponding reaction in our asimicin synthesis that proceeded with ≥20 : 1 ds. 7The erythro stereochemistry of C(23)-C(24) of aldehyde 4 requires that a syn-β-silyloxy allylsilane 6 be used in a chelate-controlled [3+2] annulation reaction with α-benzyloxy acetaldehyde (5). Initial attempts to develop an enantioselective synthesis of syn-β-silyloxy allylsilanes related to 6 focused on asymmetric allylboration reactions using (Z)-γ-dimethylphenylsilyallylboronate 7 (Scheme 1). Thus, silylcupration 9 of acetylene, addition of ‡ Address correspondence to this author at Scripps Florida, Department of Medicinal Chemistry, 5353 Parkside Drive, RF-2, Jupiter, FL 33485; e-mail: roush@scripps.edu. A more convenient route to (racemic) syn-β-hydroxyallylsilanes 8 involves the γ-silylallylstannation of aldehydes using γ-(dimethylphenylsilyl)allylstannane 9. 12 Treatment of cyclohexanecarboxaldehyde with 9 at −78 °C in CH 2 Cl 2 in the presence of BF 3 ·...

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Synthesis of (+)-Bullatacin via the Highly Diastereoselective [3+2] Annulation Reaction of a Racemic Aldehyde and a Nonracemic Allylsilane

et al. 2005

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“…3). A parallel trend is observed for MgBr2-promoted additions of cis-and trans-crotyl tributylstannanes to a-benzyloxy aldehydes but the effect is much smaller (Table 9) [18]. In such reactions the orientation of the allylic stannane and the chelated aldehyde is governed by steric effects in which the vinylic y-hydrogen orients over the five-membered chelate (Fig.…”

Section: Additions Of Trialkyl Allylic Stannanes To Aldehydes and Ketmentioning

confidence: 60%

Preparation and Addition Reactions of Allylic and Allenic Tin and Indium Reagents

Marshall¹

2000

Lewis Acids in Organic Synthesis

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“…For this purpose, the readily available γ-oxygenated allyltin compounds E-1a, [21b,23] Z1a, [23] E-1b, [21b,7a] Z-1c, [24] Z-1d, [7a] and Z-1e [7a] have been considered to evaluate their influence on the syn/anti selectivity of the allylstannation reaction, as previously observed with aldehydes (see Table 1). [6,8,9,25] …”

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confidence: 99%

syn‐Allylstannation of N‐Acyliminium Intermediates by Tributyl[γ‐(silyloxy)allyl]stannanes: A Key Reaction for the Diastereoselective Synthesis of Polyhydroxypiperidines and Polyhydroxyazepanes

et al. 2011

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Effects of Olefin Geometry on the Stereochemistry of Lewis Acid Mediated Additions of Crotylstannanes to Aldehydes

Cited by 108 publications

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Synthesis of (+)-Bullatacin via the Highly Diastereoselective [3+2] Annulation Reaction of a Racemic Aldehyde and a Nonracemic Allylsilane

Synthesis of (+)-Bullatacin via the Highly Diastereoselective [3+2] Annulation Reaction of a Racemic Aldehyde and a Nonracemic Allylsilane

Preparation and Addition Reactions of Allylic and Allenic Tin and Indium Reagents

syn‐Allylstannation of N‐Acyliminium Intermediates by Tributyl[γ‐(silyloxy)allyl]stannanes: A Key Reaction for the Diastereoselective Synthesis of Polyhydroxypiperidines and Polyhydroxyazepanes

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