61550-02-5Relevant articles and documents
Re-visiting the diastereoselectivity of organocatalytic conjugate addition of 2-trimethylsiloxyfuran to trans-crotonaldehyde
Li, Liubo,El Khoury, Anton,Clement, Brennan O.,Harran, Patrick G.
supporting information, (2021/04/22)
We describe the re-assignment of configuration previously ascribed to product diastereomers resultant from imidazolidinone-catalyzed conjugate addition of 2-trimethylsiloxyfuran to trans-crotonaldehyde. A modified procedure that uses a diphenylprolinol catalyst was subsequently developed to selectively provide the ‘syn’ diastereomeric product in high enantiomeric excess on decagram scales.
Stereoselective triplet-sensitised radical reactions of furanone derivatives
Jahjah, Rabih,Gassama, Abdoulaye,Bulach, Veronique,Suzuki, Chikako,Abe, Manabu,Hoffmann, Norbert,Martinez, Agathe,Nuzillard, Jean-Marc
supporting information; experimental part, p. 3341 - 3354 (2010/06/19)
The stereo- and regioselectivity of triplet-sensitised radical reactions of furanone derivatives have been investigated. Furanones 7a,b were excited to the 3ππ* state by triplet energy transfer from acetone. Intramolecular hydrogen abstraction then occurred such that hydrogen was transferred from the tetrahydropyran to the β position of the furanone moiety. Radical combination of the tetrahydropyranyl and the oxoallyl radicals led to the final products 8a,b. In the intramolecular reaction, overall, a pyranyl group adds to the a position of the furanone. The effect of conformation was first investigated with compounds 9a,b carrying an additional substituent on the tether between the furanone and pyranyl moiety. Further information on the effect of conformation and the relative configuration at the pyranyl anomeric centre and the furanone moiety was obtained from the transformations of the glucose derivatives 12, 14, 17 and 18. Radical abstraction occurred at the anomeric centre and at the S′-position of the glucosyl moiety. Computational studies of the hydrogen-abstraction step were carried out with model structures. The activation barriers of this step for different stereoisomers and the abstraction at the anomeric centre and at the 6' -position of the tetrahydropyranyl moiety were calculated. The results of this investigation are in accordance with experimental observations. Furthermore, they reveal that the reactivity and regioselectivity are mainly determined in the hydrogen-abstraction step. Intramolecular hydrogen abstraction (almost simultaneous electron and proton transfer) in 3ππ * excited furanones only takes place under restricted structural conditions in a limited number of conformations that are defined by the relative configuration of the substrates. It is observed that in the biradical intermediate, back-hydrogen transfer occurs leading to the starting compound. In the case of glucose derivatives, this reaction led to epimerisation at the anomeric centre.
Total synthesis of (+)-azaspiracid-1. An exhibition of the intricacies of complex molecule synthesis
Evans, David A.,Kvaerno, Lisbet,Dunn, Travis B.,Beauchemin, Andre,Raymer, Brian,Mulder, Jason A.,Olhava, Edward J.,Juhl, Martin,Kagechika, Katsuji,Favor, David A.
supporting information; experimental part, p. 16295 - 16309 (2009/05/08)
The synthesis of the marine neurotoxin azaspiracid-1 has been accomplished. The individual fragments were synthesized by catalytic enantioselective processes: A hetero-Diels-Alder reaction to afford the E- and HI-ring fragments, a carbonyl-ene reaction to furnish the CD-ring fragment, and a Mukaiyama aldol reaction to deliver the FG-ring fragment. The subsequent fragment couplings were accomplished by aldol and sulfone anion methodologies. All ketalization events to form the nonacyclic target were accomplished under equilibrating conditions utilizing the imbedded configurations of the molecule to adopt one favored conformation. A final fragment coupling of the anomeric EFGHI-sulfone anion to the ABCD-aldehyde completed the convergent synthesis of (+)-azaspiracid-1.
