Silylene transfer to α-keto esters and application to the synthesis of γ-lactones

Howard, Brett E.; Woerpel, K. A.

doi:10.1016/j.tet.2009.05.066

Cited by 15 publications

(5 citation statements)

References 27 publications

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“…The synthetic routes reported so far made use of different approaches, such as three‐component reactions starting from aldehydes or ketones (Scheme , paths a , b ),7,8 the gold‐catalyzed tandem cycloisomerization/oxidation of homopropargylic alcohols ( path c )9 and the AgOTs‐catalyzed silylene transfer to α‐keto esters followed by an iodolactonization reaction ( path d ) 10. Other methods include the SmI 2 ‐promoted opening‐lactonization of γ‐epoxy esters,11 the asymmetric Michael addition of α,α‐disubstituted aldehydes to maleimides,12 the [Cu(acac) 2 ]‐catalyzed 1,5‐electrocyclic ring closure of conjugated esters with dimethyl diazomalonate13 and the reduction of γ‐acylsuccinates 14…”

Section: Methodsmentioning

confidence: 99%

Flow Synthesis of Substituted γ‐Lactones by Consecutive Photocatalytic/Reductive Reactions

et al. 2014

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Section: Methodsmentioning

confidence: 99%

Flow Synthesis of Substituted γ‐Lactones by Consecutive Photocatalytic/Reductive Reactions

et al. 2014

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“…While the standard Ireland−Claisen rearrangement is performed by sequential enolization and silylation of allylic esters, alternative approaches to the requisite silyl ketene acetal have been reported. Methods include 1,4-addition to enoates, and silylene transfer followed by 6π-electrocyclization, or by Rh-catalyzed reduction of enoates . These methods allow for the generation of chiral products from achiral starting materials; however, a method that introduces multiple α substituents in a single-pot process could potentially allow a more rapid buildup of molecular complexity.…”

mentioning

confidence: 99%

Synthesis of γ,δ-Unsaturated Glycolic Acids via Sequenced Brook and Ireland−Claisen Rearrangements

Schmitt

Johnson

2010

Org. Lett.

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Organozinc, magnesium, and lithium nucleophiles initiate a Brook/Ireland-Claisen rearrangement sequence of allylic silyl glyoxylates resulting in formation of γ,δ-unsaturated α-silyloxy acids.New methods to produce the glycolic acid moiety continue to be important in the creation of small molecule building blocks. 1 γ,δ-Unsaturated glycolic acid derivatives represent a functional group-rich subset of substituted α-hydroxy acids with significant potential for further elaboration. The preparation of such compounds may be achieved via Ireland-Claisen rearrangement of allyl glycolate esters. 2 While the standard Ireland-Claisen rearrangement is performed by sequential enolization and silylation of allylic esters, alternative approaches to the requisite silyl ketene acetal have been reported. Methods include 1,4-addition to enoates, 3 silylene transfer followed by 6π-electrocyclization, 4 or by Rh-catalyzed reduction of enoates. 5 These methods allow for the generation of chiral products from achiral starting materials; however, a method that introduces multiple α-substituents in a single-pot process could potentially allow more rapid buildup of molecular complexity. An assessment of other Grignard reagents revealed that MeMgBr had potential as an effective nucleophile as it cleanly added to cinnamyl silyl glyoxylate 1a at 0 °C. In this case, Brook rearrangement did not occur below room temperature. When the reaction was allowed to warm, only decomposition was observed. Silyl ketene acetal formation was then attempted by addition of MeMgBr at 0 °C followed by warming to room temperature and addition of TMSCl; however, this also resulted in decomposition. Given that no TMS incorporation had occurred, we turned to TMSOTf, which induced the desired Ireland-Claisen rearrangement and provided the γ,δ-unsaturated glycolic acid 7 in 55% yield ( Organozinc nucleophiles were also found to be effective. ZnEt 2 serves as an efficient hydride donor, triggering the sequential Brook and Ireland-Claisen rearrangements, to afford the glycolic acid in 69% yield with good diastereoselectivity (Table 1, entry 5). The reduction of α-ketoesters with ZnEt 2 or EtMgBr has been previously reported; however, it is typically a minor byproduct to ethyl addition. 9 Allyl zinc bromide and allenyl zinc bromide were useful triggers as well (Table 1, entries 6-10).Substituted allylic zinc nucleophiles were also competent initiators. Methallyl zinc bromide provided the desired products with slightly diminished diastereoselectivity relative to allyl zinc bromide (Table 1, entries 11-12). The reaction was also tolerant of crotyl-and cinnamylzinc reagents; however, products were obtained as a complex mixture of diastereomers (not shown). Notably, none of the organozinc nucleophiles required silyl ketene acetal formation, as the zinc enolate underwent [3,3]-rearrangement spontaneously. Geranyl silyl glyoxylate 20 underwent the title transformation when treated with allenyl or allylic zinc bromides, providing glycolic acid derivatives in moderat...

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“…Thus, only the 2-alkoxyoxetane 2OX has been observed in the Paternò–Büchi reactions reported so far [ 19 – 27 ]. Thus, in this study, furan-2-ylmethyl 2-oxoacetates 1a , b and 2-(furan-2-yl)ethyl 2-oxo-2-phenylacetate 1c [ 28 ] were synthesized, in which the furan ring and the carbonyl moiety are connected intramolecularly, and their photochemical reactions were investigated to see whether the reaction proceeds intramolecularly to produce the 3-alkoxyoxetane derivative A and/or the dioxabicyclo[2.2.1]hept-5-ene derivative B , or intermolecularly to give the 2-alkoxyoxetane derivative C ( Scheme 2 ).…”

Section: Resultsmentioning

confidence: 92%

“…Compounds 1a – c [ 28 ] were synthesized from furan-2-ylmethanol or furan-2-ylethanol [ 29 ] ( Scheme 3 ). Compound 1a (R = Ph) was irradiated in degassed benzene with a high-pressure Hg lamp with a Pyrex filter ( Scheme 3 ).…”

Section: Resultsmentioning

confidence: 99%

Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction

Arimura¹,

Mizuta

Hiraga

et al. 2011

Beilstein J. Org. Chem.

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SummaryFuran-2-ylmethyl 2-oxoacetates 1a,b, in which the furan ring and the carbonyl moiety were embedded intramolecularly, were synthesized from commercially available furan-2-ylmethanol and their photochemical reaction (hν > 290 nm) was investigated. Twelve-membered macrocyclic lactones 2a,b with C i symmetry including two oxetane-rings, which are the Paternò–Büchi dimerization products, were isolated in ca. 20% yield. The intramolecular cyclization products, such as 3-alkoxyoxetane and 2,7-dioxabicyclo[2.2.1]hept-5-ene derivatives, were not detected in the photolysate.

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Silylene transfer to α-keto esters and application to the synthesis of γ-lactones

Cited by 15 publications

References 27 publications

Flow Synthesis of Substituted γ‐Lactones by Consecutive Photocatalytic/Reductive Reactions

Flow Synthesis of Substituted γ‐Lactones by Consecutive Photocatalytic/Reductive Reactions

Synthesis of γ,δ-Unsaturated Glycolic Acids via Sequenced Brook and Ireland−Claisen Rearrangements

Formation of macrocyclic lactones in the Paternò–Büchi dimerization reaction

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