16838-46-3Relevant academic research and scientific papers
PtCl2-mediated cycloisomerization of unsaturated propargylic carboxylates
Anjum, Shazia,Marco-Contelles, José
, p. 4793 - 4803 (2007/10/03)
The PtCl2-mediated cycloisomerization of unsaturated propargylic carboxylates yields differently functionalized bicyclo[4.1.0]heptane enol esters from moderate to good yield, in a very diastereoselective manner. We have prepared and submitted to PtCl2-catalyzed cycloisomerization a series of differently substituted hept-1-en-6-ynes with different O-acyl (acetyl, trichloroacetyl, 3,4,5-trimethoxybenzoyl, etc.) protecting groups at propargylic positions, investigating also the effect of the geometry at the double bond, as well as the effect of the number of substituents at the alkene moiety. As a result, we have found that the O-acetyl migrating group is the best one in terms of simplicity and chemical yields. In this reaction we have isolated mixtures of compounds formed by minor 1-acetoxy-allenes and major bicyclo[4.1.0]heptane derivatives. Major products are the result of a sequential process involving steps of cycloisomerization plus cyclopropanation, followed by acyl migration. The basic methanolysis (K2CO3, MeOH) of these intermediates gave mixtures of cis and trans-caran-2-ones. This two-step protocol (cycloisomerization plus basic methanolysis) for the syntheses of α,β-unsaturated cyclopropyl ketones constitutes a synthetic alternative to the usual unfriendly, intramolecular cyclopropanation of unsaturated α-diazocarbonyl derivatives. The formation of these bicyclo[4.1.0]heptane derivatives is a simple, but efficient entry into the skeleton of the 'carane' family of natural products.
Conformation of Epi-α-cyperone and Related Enones
Huffman, John W.,Swain, William E.,Jacobus, John,McPhail, Andrew T.
, p. 3088 - 3096 (2007/10/02)
The conformations of epi-α-cyperone (10-epieudesma-4,11-dien-3-one, 2) and its dihydro and 14-nor analogues (4 and 15, respectively) have been investigated by a combination of lanthanide induced shift reagent 1H NMR, 13C NMR, and high field 1H NMR techniques.Comparison of these spectral data with those of the normal eudesmane derivatives, α-cyperone (1), dihydro-α-cyperone (3), and 14-noreudesm-4-en-3-one (14) clearly shows that the conformations of all six enones are similar with a half-chair conformation for ring A and a chair conformation for ring B.11-Methyl-10-epieudesm-4-en-3-one (5) was prepared either from 5α-hydroxy-10-epieudesm-11-en-3-one (6) or by the Robinson annulation of 2-methyl-5-tert-butylcyclohexanone with ethyl vinyl ketone. 14-Nor-11-methyl-10-epieidesm-4-en-3-one (15) was prepared by the annulation of 2-methyl-5-tert-butylcyclohexanone with methyl vinyl ketone.The 13C lanthanide induced shift and high-field 1H NMR spectra of enones 5 and 13 indicate that these molecules are not conformationally homogeneous.An X-ray structure determination of the oxime of enone 5 showed that in the solid state ring A exists in a envelope conformation and ring B in a twist conformation with a ψ-equatorial tert-butyl group.Crystals of the oxime of 5 belong to the triclinic system, space group P1, with a = 6.290(3) Angstroem, b = 12.010(5) Angstroem, c = 10.341(5) Angstroem, α = 85.20(2) deg, β = 95.56(2) deg, γ = 101.09(2) deg, and Z=2.Atomic positional and thermal parameters were refined by least-squares calculation to R = 0.068 over 1609 observed reflections measured by a diffractometer.
