Free accessResearch articleFirst published online 1999-5
Tandem 5- Exo -dig-5- exo -trig Radical Cyclization leading to a 6,5-Ring Fused Carbobicycle possessing Two Contiguous Quaternary Carbons at the Bridgehead and its Adjacent Positions †
The tin-mediated tandem 5-exo-dig-5-exo-trig radical cyclization of dibromoacetal 4a stereoselectively gives the angular 6,5,5-ring fused tricycle 6via spirocyclic acetal 5 in 93% yield.
References
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The bromoacetalization of the mixture of 3E and 3Z (1.3:1) obtained by the Wittig reaction of 2 (0.05 mol dm−3) gave 4a in a similar yield: MaryanoffB. E. and ReitaA. B.Phosphorus Sulfur, 1986, 27, 167.
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Crystal Data for 4a: C14H20Br2O2, Mr = 380.1, monoclinic space group P21, a = 10.519(5), b =12.038(6), c = 6.463(3) Å, β = 98.51(4)°, V = 809.4(7) Å3, Z = 2, Cu-Kα radiation, λ = 1.54184 Å, T = 293 K, μ = 63.01 cm−1, 1338 reflections measured, 1216 unique reflections, 679 observed reflections [I > 2σ(I)], R = 0.089. Full crystallographic details, excluding structure factors, have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Research (S), 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 423/20.
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No attempt was made to determine the stereochemistry of the inseparable dibromoacetals and cyclization products.
11.
The tandem radical cyclization of the homologous dibromoacetals derived from cycloheptanone gave three 5-exo-dig-5-exo-trig and two 5-exo-dig-6-(formal)-endo-trig cyclization products in moderate yield. The reaction of the dibromoacetals derived from cyclopentanone with Bun3SnH gave two 5-exo-dig-5-exo-trig and a 5-exo-dig-6-(formal)-endo-trig cyclization products.
