Fluoronaphthalene Building Blocks via Arynes: A Solution to the Problem of Positional Selectivity

Abstract

When 3‐fluoro‐ and 3‐chloro‐1,2‐didehydrobenzenes are generated in the presence of 2‐(trimethylsilyl)furan, two regioisomeric cycloadducts are formed in a 1:2 ratio. However, regioselectivity can be installed by fitting one bulky trimethylsilyl group into sterically critical positions of each of the two reaction components. Thus 3‐fluoro‐6‐trimethylsilyl‐1,2‐didehydrobenzene and 2‐(trimethylsilyl)furan give one cycloadduct exclusively. In this way, the Diels–Alder reaction between suitably adorned arynes and similarly designed furans can open an entry to naphthalene derivatives that have unprecedented substituent patterns that qualify them as building blocks for pharmaceutical or agricultural research. The acid‐catalyzed isomerization of model 1,4‐epoxy‐1,4‐dihydronaphthalenes, the aryne/furan cycloadducts, exhibits unexpected effects on rates and regioselectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Are reactions between allylpotassiums and halotrimethylsilanes diffusion-controlled?

“…For laboratory routine and abbreviations, see an earlier publication 30 6-dimethylbicyclo[3.1.1]hept-2-en-2-ylmethyl)silane (1a). Butyllithium (50 mmol) in hexane (30 mL) was added to a solution of potassium tert-butoxide (5.6 g, 50 mmol) and (-)-β-pinene (8.0 mL, 6.8 g, 50 mmol) in tetrahydrofuran (50 mL) kept in a dry ice/toluene bath.…”

Total Syntheses of Cytotoxic, Naturally Occurring Kalasinamide, Geovanine, and Marcanine A

“…Consequently the desired product 16 is formed with high selectivity. [21] Traces of the undesired isomer could be easily removed by recrystallization.…”

CF3‐Bearing Aromatic and Heterocyclic Building Blocks

“…In fact, the aryne route to (trifluoromethyl)naphthalenes and congeners [38] proved to be as expedient as the previously explored routes for the preparation of (trifluoromethoxy)naphthalenes [39] and fluoronaphthalenes. [40] After lithiation of 2-chlorobenzotrifluoride at the position adjacent to Cl, [41] the cold solution (À75 8C) is siphoned through teflon tubing into furan which is kept at ambient temperature. Immediate b elimination of lithium chloride liberates 1,2-didehydro-3-(trifluoromethyl)-benzene, which instantaneously undergoes [4+2] cycloaddition to afford 1,4-epoxy-1,4-dihydro-5-(trifluoromethyl)naphthalene (6; 76 % yield; Scheme 4).…”