New Highly Strained Multifunctional Heterocycles by Intramolecular Cycloadditions of Nitrones to Bicyclopropylidene MoietiesFor one of us (A. d. M.) this article is to be counted as Part 132 in the series “Cyclopropyl Building Blocks for Organic Synthesis”. For Part 131 see: V. Bagutski, N. Moszner, F. Zeuner, U. K. Fischer, A. de Meijere, Adv. Synth. Catal.2006, in press. Part 130: F. Brackmann, C. Cabrele, A. de Meijere, Eur. J. Org. Chem.2006, in press.

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 %). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)