Ring Expansion and Contraction of a Two-Carbon Bridged Spiropentane

Abstract

The reactions of tricyclo[4.1.0.01,3]heptan-4-one (5) and two related systems with diazomethane and m-CPBA were examined in order to determine the relative reactivity and migratory aptitudes for the three compounds. The reactions of 5 with diazomethane and m-CPBA yielded new derivatives of the tricyclo[5.1.0.01,3]octane ring system that showed that migration of cyclopropylcarbinyl is favored over cyclopropyl migration in this system. Photolysis of 5-diazotricyclo[4.1.0.01,3]heptan-4-one (23) in methanol and dimethylamine did not lead to ring contraction to the tricyclo[3.1.0.01,3]hexane ring system, but an interesting product was derived from an unusual rearrangement process in the photolysis in dimethylamine. Matrix photolysis of 23 at 15 K gave a decrease in the diazo band at 2085 cm-1 and the appearance of a new band at 2117 cm-1, which is a normal position expected for a small-ring ketene such as cyclopropylketene. Thus, matrix photolysis appears to have yielded a derivative of the previously unknown tricyclo[3.1.0.01,3]hexane ring system. The lithium enolate of 5 was characterized by NMR spectroscopy at −80 °C and was found to rearrange to m-cresol at −65 °C. The geometries of the bridged spiropentanes of this work were optimized at the MP2(frozen core)/6-31G* level of theory, and group equivalent values were derived in order to calculate the heats of formation for these compounds using the calculated energies.

Non-classical structures of organic compounds: unusual stereochemistry and hypercoordination

“…Angular parameters characterising the configuration of the quaternary carbon atom in molecules 52 ± 55 and strain energies of these structures found by MP2/6-31G** ab initio calculations. 101 nate carbon atoms, the only other non-classical topological form is represented by structure 57 with an inverted configuration of bonds at the carbon atom.…”

The First Enantiomerically Pure [n]Triangulanes and Analogues: σ-[n]Helicenes with Remarkable Features

“…[7] Since intramolecular cyclopropanations of a remote double bond in alkenyl diazoacetate catalyzed by a dirhodium tetrakis(carboxamidate) with chiral ligands have been demonstrated to proceed with high diastereoselectivities, [8] we examined this type of reaction for (2-methylenecyclopropyl)methyl diazoacetate (10), prepared from (2-methylenecyclopropyl)methanol (6) and NBoc-glycine (7) (Scheme 1), utilizing the [Rh 2 (5R-MEPY) 4 ] catalyst. [8] Unfortunately, this approach to the tricyclic lactone 11 turned out to be not more efficient than the previously reported one: [9] the yield in the cyclization step was only 7 % of almost racemic 11 (ee 10 %), the structure of which was confirmed by X-ray crystallography (Figure 1). [10] Other appropriate enantiomerically pure starting materials for the preparation of (M)-or (P)-3 and 4 were obtained from racemic bicyclopropylidenecarboxylic acid (rac-12), which is easily available from the multifunctional C 6 -building block bicyclopropylidene [11] by deprotonation and carboxylation, [12] and from racemic exo-dispiro[2.0.2.1]heptane-1-carboxylic acid (rac-13).…”

14‐Methylpentadecano‐15‐lactone (Muscolide): A New Macrocyclic Lactone from the Oil of Angelica archangelica L.

“…Unequivocal identification of muscolide (1) in Angelica root oil was achieved by coinjection with an authentic (racemic) sample synthesized in our laboratory, and by comparison of their mass spectra. The Baeyer ± Villiger oxidation of commercially available muscone to muscolide was performed in one step according to the procedure of Wiberg and Snoonian [15]. The reaction was extremely slow, and only 12% of muscone was converted to 1 within 18 h. This is the first report of the occurrence of muscolide (1) in a natural product.…”