Intramolecular cycloadditions of various nitrone functionalities with different substituents (R = Me, Bn, tBu) at the nitrogen atom tethered to a bicyclopropylidene unit through a two-carbon chain led to cis-fused tricyclic isoxazolidines (3- alkyl-3,3a,4,5,5a,6-hexahydrocyclopropa[2,3]cyclopenta[1,2- c]isoxazolespiro[1,1]cyclopropanes) 26 in 42–58% yield with complete regio- and diastereoselectivity. The thermal rearrangement of the cycloadducts 26 under neutral conditions afforded the corresponding tricyclic tetrahydropyridones 27 (52–53%). The analogous starting materials with a three-carbon tether, the 4-(bicyclopropyliden-2-yl)butylidenenitrones furnished tricyclic isoxazolidines 28 (54–58%) and tetrahydropyridones 29 (55–64%) by subsequent thermal rearrangement. Under acidic conditions (TFA), the cycloadducts 26 and 28 underwent fragmentative rearrangements to afford the tricyclic β-lactams 30 and 32 (50–66%), respectively, of which the former suffered amide-bond cleavage in situ to provide the corresponding N-trifluoroacetyl β-amino acid derivatives 31 (68–71%).
New Highly Strained Multifunctional Heterocycles by Intramolecular Cycloaddition of Nitrones to Bicyclopropylidene Moieties / M. Marradi; A. Brandi; J. Magull; H. Schill; A. de Meijere. - In: EUROPEAN JOURNAL OF ORGANIC CHEMISTRY. - ISSN 1434-193X. - STAMPA. - 2006:(2006), pp. 5485-5494. [10.1002/ejoc.200600417]
New Highly Strained Multifunctional Heterocycles by Intramolecular Cycloaddition of Nitrones to Bicyclopropylidene Moieties
M. Marradi;A. Brandi;
2006
Abstract
Intramolecular cycloadditions of various nitrone functionalities with different substituents (R = Me, Bn, tBu) at the nitrogen atom tethered to a bicyclopropylidene unit through a two-carbon chain led to cis-fused tricyclic isoxazolidines (3- alkyl-3,3a,4,5,5a,6-hexahydrocyclopropa[2,3]cyclopenta[1,2- c]isoxazolespiro[1,1]cyclopropanes) 26 in 42–58% yield with complete regio- and diastereoselectivity. The thermal rearrangement of the cycloadducts 26 under neutral conditions afforded the corresponding tricyclic tetrahydropyridones 27 (52–53%). The analogous starting materials with a three-carbon tether, the 4-(bicyclopropyliden-2-yl)butylidenenitrones furnished tricyclic isoxazolidines 28 (54–58%) and tetrahydropyridones 29 (55–64%) by subsequent thermal rearrangement. Under acidic conditions (TFA), the cycloadducts 26 and 28 underwent fragmentative rearrangements to afford the tricyclic β-lactams 30 and 32 (50–66%), respectively, of which the former suffered amide-bond cleavage in situ to provide the corresponding N-trifluoroacetyl β-amino acid derivatives 31 (68–71%).File | Dimensione | Formato | |
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