Reaction of tin enolates with substituted tricarbonylcyclohexadienyliumiron hexafluorophosphate electrophiles: diastereoselective synthesis of (±)-trichodiene

Abstract

A number of tin enolates react cleanly with tricarbonylcyclohexadienyliumiron cations, in cases where the use of lithium enolates or silyl enol ethers is problematic; this new carbon-carbon bond-forming reaction allows diastereoselective construction of proximate quaternary centres and provides a key step in a short synthesis of (_+I-trichodiene.

Intramolecular hydrogen exchange among the coordinated methane fragments of Cp2W(H)CH3. Evidence for the formation of a .sigma. complex of methane prior to elimination

“…We also measured A:CHj_H and kCD¡_O carefully at 72.6 °C in CD3CN and compared them to each other. The isotope effect was inverse, with &ch,-h/&cd3-d equal to 0.75 (4).…”

“…;2-CH3CN) (25 mg, 7.04 X 10"5 mol, 48%) as an orange solid. *H NMR (C6D6): 4.12 (Cp), 2.58 (CH3). MS: m/e 3 5 5 (,84W).…”

“…Gas samples were then removed by syringe and injected into the mass spectrometer. The percentages of isotopically labeled methanes calculated by methnal from the intensities of the hydrocarbon fragments at m/e 12-20 were the following: CH4, 9 (4); CH3D, 17 (5); CH2D2, 24 (6); CHD3, 35 (4); CD4, 15 (4).…”

“…W(D)12CH3 + W(D)12CH2D + W(D)12CHD2 + W(DAlthough K¡ had been most accurately determined at 45.0 °C, showed no temperature dependence greater than experimental error between 40 and 50 °C; we therefore took as 1 4. (2) at 47.3 °C, the temperature of the double-labeling Cp2W(H)13CH3/Cp2W(H)CD3 experiment.…”

“…Samples were removed from the baths at intervals and cooled to room temperature prior to analysis by NMR. Spectra were taken to cover 2-3 half-lives of the reaction, with approximately [3][4][5] points/half-life. The rate constants in Table IV for the elimination of methane from Cp2W(H)CH3 were determined by NMR as follows: at 80.5 °C, the integrals of both the hydride (<5 -10.57) and the methyl peak ( 0.03) vs the internal standard cyclohexane were measured for each point; at the other temperatures, the height of the methyl resonance was compared with that of the cyclohexane internal standard.…”