Angela Maria Celli

Synthesis of furo-furans by rearrangement of 4-acetylpyrans

Abstract The hetero-Diels-Alder reaction of 1-oxabutadienes 1a–c bearing electron-withdrawing groups with ethyl vinyl ether and 2,3-dihydrofuran gave the functionalized 5,6-dihydro-4H-pyrans 2a-c, 4c and 4H-4a, 5, 6, 6a-tetrahydrofuro[2,3-b]pyrans 5a-c and 6c. Cycloadducts 2a and 4c easily rearranged to furo[2,3-b]furans 3a, 3c and 9c and cycloadducts 5a and 6c to difuro[2,3-b:3′,4′-d]furans 7a, 7c and 8c. The stereochemistry of compounds 5c and 7a was determined by single crystal X-ray analysis. Relative configurations of the other compounds were established by nOe data. Some aspects of the reaction mechanisms are discussed.

Spiro-dihydrofuran-pyrazolidinones from tetraacetylethylene andazo-dicarbonyl compounds

Abstract Tetraacetylethylene (1) reacted with electron-withdrawing azo compounds to give spiro furan-pyrazoles. Their structure was confirmed by an X-ray crystallographic analysis on a derivative of the spiro furan-3(2H),5′(7′H)-pyrazolo 1,2-a∥1,2,4 triazole-1′,3′,6′-trione. The cycload-ducts show ring-open chain tautomerism.

A new route to highly substituted 1H-pyrrol-3(2H)-ones

Abstract Reaction of 3,4-diacetyl-3-hexen-2,5-dione, 1, with alkyl or aryl primary amines, 2a–g, led to highly substituted 1H-Pyrrol-3(2H)-ones, 3a–g. The structure was established from a single crystal X-ray analysis of compound 3c.

Hydrogen-bonding pathways affecting chemical reactivity of mandelylasparagine and related compounds

The different behaviour of L-(+)-N-mandelyl-L-(–)-asparagine, N-mandelyl-2-amino-4-pentanoic acid and N-mandelyl-2-aminobutanoic acid towards acylation was considered. 13C and 1H n.m.r. non-selective and selective relaxation rates and 1H-{1H} n.O.e.s were taken to show that L(+)-N-mandelyl-L-(–)-asparagine assumes, in DMSO solution, a conformation quite different from that of the other two amino acids. In this conformation both lone pairs of the alcoholic oxygen were shown to be involved in hydrogen bonding and to be shielded in a way that makes approach of the acylating reagent difficult.