The intramolecular and intermolecular geometries of six thiophenes carrying oxygen-containing substituents have been determined. Crystals of 2-methoxythiophene and 3-methoxythiophene were grown in situ on a diffractometer from liquid samples. The 2-methoxy group introduces significant distortions to the thiophene nucleus and each molecule participates in four S.O contacts leading to an infinite bilayer. The extended structure of 3-methoxythiophene comprises zigzag chains of molecules linked by S.O contacts. Molecules of 2-acetyl-3-methoxythiophene are arranged in pairs about inversion centres, with ring centroids 3.835 Å apart. 5-Cyano-3-hydroxythiophene adopts the hydroxythiophene tautomeric form which allows conjugation between the S atom and the nitrile group: O-H.N hydrogen bonding leads to chains which are cross-linked by S.O contacts to give infinite two-dimensional layers. 5-(Methylthio)thiophen-3(2H)-one exists exclusively as the thiophen-3(2H)-one form in the solid state, allowing maximum conjugative interaction of both the ring heteroatom and the substituent with the carbonyl group: each molecule is linked to two of its neighbours through pairwise C-H.O interactions, forming ribbons. Spiro[cyclohexane-1,2'-2',3'-dihydrothiophen]-3'-one crystallizes with four independent molecules in the asymmetric unit with only minor differences between these: the five- and six-membered rings in each molecule are approximately orthogonal and C-H.O hydrogen bonding generates chains. The last two structures differ from the others in that they lack a fully aromatic thiophene system.
XtalFluor-E® has been extensively used in a broad range of reactions in the past few years. Here we report its use with protic nucleophiles in a catalytic manner for the in situ generation of protons that lead to the proteo functionalization of activated olefins. Utilizing the latter protocol, proteo etherification of enamides gives rise to N,O-acetals in nearly quantitative yields.
Methoxymethylene Meldrum's acid 1 reacts with 5- and 6-membered lactams in refluxing acetonitrile to give the N-substituted products 9-15. If the reactions are continued for extended times, the Meldrum's acid derivatives decompose to provide enamidoesters e.g. 22-24. Flash vacuum pyrolysis of the 5-membered ring products 9-13 provides reasonable yields of the fused pyrrolones 31-35. The constitution of the products is supported by X-ray crystal structures of 10, 12, 19, 32 and 34.
The structures of two derivatives of Meldrum's acid, 2,2-dimethyl-5-[N-(1-pyrrolyl)aminomethylene]-l,3-dioxane-4,6-dione, ClIH12N204, (1), and 2,2-dimethyl-5-[N-(1-pyrazolyl)aminomethylene]-l,3-dioxane-4,6-dione, C10HIlN304, (2), which differ only at one position in the five-membered ring, are described.
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