Three eremophilanolides, 1alpha-acetoxy-8beta-methoxy-10betaH-eremophil-7(11)-en-8alpha,12-olide (1); 1alpha-angeloyloxy-6beta-hydroxy-8beta-methoxy-10betaH-eremophil-7(11)-en-8alpha,12-olide (2); and 1alpha-angeloyloxy-8betaH,10betaH-eremophil-7(11)-en-8alpha,12-olide (3), and two pyrrolizidine alkaloids, integerrimine (4) and its N-oxide (5), were isolated from bioactive fractions of Senecio miser. The structures of the new compounds 1 and 2 were established by NMR spectroscopic analysis and chemical transformation. The X-ray analysis of compound 1 was also performed. Eremophilanolides 1 and 2 and alkaloids 4 and 5 were found to be strong insect antifeedants, further supporting a proposed defensive role for these classes of compounds.

Water molecules confined inside narrow pores are of great importance in understanding the structure, stability, and function of water channels. Here we report that besides the H-bonding water that structures the pore, the permanent presence of a significant, fast-moving fraction of incompletely H-bonded water molecules inside the pore should control the free entry and exit of water. This is achieved by means of complementary DSC and solid-state NMR studies. We also present compelling evidence from X-ray diffraction data that the cluster formed by six water molecules in the most stable cage-like structure is sufficiently hydrophobic to be stably adsorbed in a nonpolar environment.

[reaction: see text] A new iron(III) halide-promoted aza-Prins cyclization between gamma,delta-unsaturated tosylamines and aldehydes provides six-membered azacycles in good to excellent yields. The process is based on the consecutive generation of gamma-unsaturated-iminium ion and further nucleophilic attack by the unsaturated carbon-carbon bond. Homoallyl tosylamine leads to trans-2-alkyl-4-halo-1-tosylpiperidine as the major isomer. In addition, the alkyne aza-Prins cyclization between homopropargyl tosylamine and aldehydes gives 2-alkyl-4-halo-1-tosyl-1,2,5,6-tetrahydropyridines as the only cyclic products.

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The design concept of functional solids relies on controlling the topology of crystal packing through exploitation of weak intermolecular forces. In the context of cyclic aggregates, the ability to anticipate the consequences of ring constituents and their stereochemistries on ring conformation is vitally important since even an apparently slight structural change effected on molecules can dramatically alter the crystal structure. We have found that solid-state structures formed by hydroxy acids with a general structure (+/-)-1 depend on steric interactions. Thus, with the exception of molecules 1b and 1e, compounds (+/-)-1a-(+/-)-1m, which possess bulky and conformationally rigid substituents, aggregate by forming tapes and sheets by alternating (+) and (-) subunits held together through carboxylic acid-to-alcohol hydrogen bonds. Homologue (+/-)-1n, with conformationally flexible substituents which allow conformational deformation, gives, by incorporation of molecules of water, an efficient hexagonal assembly which extends to the third dimension to form tubular H-bonding networks. Each puckered channel can be described as interconnected closely packed hexagons in chairlike conformations. The ethyl groups presented in (+/-)-1n gave the volume required to lock the inner hexagonal wall into a rigid structure. Attempts to obtain cyclic aggregates using small substituents, compounds (+/-)-1o-(+/-)-1q, failed. The observed supramolecular assemblies of the anhydrous compounds can be classified into one-dimensional strands and two-dimensional sheets, while three-dimensional networks are present only in the hydrated molecules (1b, 1e, and 1n). The crystal structure of the anhydrous (+/-)-1n compound confirms the important role played by water molecules in the formation of tubular structures.

Domino processes have received great attention from the chemical community because they address fundamental principles of synthetic efficiency and reaction processing. 1 Over the last four years, we have been involved in a research program aimed at developing metal-free and diversity oriented domino-based syntheses of biologically relevant heterocyclic scaffolds. 2 Our design principle is based on the expected multiplicative effect on molecular complexity achieved by a chain of two or more coupled domino processes in the same reaction vessel. This approach requires a careful design of each of the participant domino processes. To be coupled in a chain manner, each domino process must generate a suitably functionalized molecule able to be simultaneously engaged in the subsequent complexity-generating domino process and so on. Additionally, the whole process would be performed in a format amenable for application in combinatorial chemistry. Experimentally, the transformation of this concept in a one synthetic step strategy is not a simple task due to the unattainable kinetic tuning of each of the numerous chemical reactions involved. A more feasible approach should consist in the transformation of this concept in a one-pot synthetic strategy. In this new scenario, the consecutive coupled domino processes should be performed one at a time and linked in a onepot operation. In a first experimental approach, we chose the simple model shown in eq 1, addressing the synthesis of polysubstituted pyrroles. The protocol combines two coupled domino processes: the trialkylamine-catalyzed synthesis of enolprotected propargylic alcohols 1 2 (domino I) and their sequential transformation into pyrroles 3 (domino II). The key for this transformation came from a serendipitously discovered spontaneous rearrangement of 1,3-oxazolidines 2 to pyrroles 3.Polysubstituted pyrroles are common pharmacophores of numerous natural antibiotics and alkaloids 3 and they have also found applications in the field of material chemistry. 4 These properties are of considerable interest in the development of new efficient syntheses of these heterocycles. Among the plethora of methods available for pyrrole construction, 3 metal-based strategies 5 and 1,3-dipolar cycloadditions 6 have concentrated the most attention. In contrast, the number of examples reported in the literature dealing with metal-free, modular and direct syntheses of these heterocycles is scarce. 7 Therefore, there is a clear demand for new metal-free, modular and direct synthetic protocols with atom-economy, easy reaction processing, general applicability and environmental care performance.1,3-Oxazolidines 2 are readily obtained in a one-pot manner by the ytterbium-catalyzed reaction 8 of the conjugated alkynoates 1 and primary amines (eq 2). Pure 1,3-oxazolidines 2 rearrange to pyrroles 3 when they are stored on the bench without solvent (eq 2). This rearrangement is very slow at room temperature and needs months to be completed. 9 While heating speeds up this process from months to ...

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