Studies on the Oxidative Addition Reaction of 1,1-Dibromo-1-alkenes, α-Dehalopalladation, and the Intramolecular Bis(carbopalladation) Reaction of Alkenes. An Efficient Entry to Fused Bicycles

• Published in: Journal of organic chemistry Vol. 65; no. 25; pp. 8532 - 8543
• Main Authors: Ma, Shengming, Xu, Bin, Ni, Bukuo
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 15.12.2000; Amer Chemical Soc
• Subjects: Chemistry; Chemistry, Organic; Physical Sciences; Science & Technology; ORGANOBORON COMPOUNDS; CROSS-COUPLING REACTIONS; UNSATURATED CARBENES; DIELS-ALDER REACTION; POTASSIUM TERT-BUTOXIDE; PHASE-TRANSFER CONDITIONS; ORGANIC HALIDES; HIGHLY STEREOSELECTIVE SYNTHESIS; PALLADIUM-CATALYZED VINYLATION; C-H INSERTION
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo005542d

Twenty-three examples of 1,1-dihalo-1-alkenes were synthesized by the conventional alkylation methods. The oxidative addition reactions of 1,1-dibromo-2,2-diphenylethene or 1,1-dibromo-2-phenylpropene with a stoichiometric amount of Pd(PPh3)4 afforded 1,2-diphenylacetylene and 1-phenylpropyne, respectively, indicating that α-dehalopalladation reaction occurred to afford vinylic carbene intermediates. However, α-dehalopalladation reaction was not observed in all 1,1-dihalo-1-alkenes containing an extra CC bond suitable for cyclic carbopalladation under the current reaction conditions probably due to the fast cyclic carbopalladation reaction of 40A-type of palladium intermediates; A series of bicycles, i.e., fused 5,6-, 6,6-, 6,7-, and 7,7-bicyclic compounds, were prepared efficiently via this bicyclic carbopalladation protocol. Under condition A, within 0.5 h, 10 afforded the monocyclic product 37 in 79%. With prolonged reaction time, 37 was converted to bicycle 36. Even with isolated 37, the corresponding reaction under condition A afforded 36 in 92% NMR yield, indicating a stepwise oxidative addition−cyclic carbopalladation−β-elimination mechanism for this bicyclization reaction.