Reactions of Ruthenium Complexes with Propargylic Compounds Containing a Cyclobutyl Group
Date Issued
2012
Date
2012
Author(s)
Wang, yung-ching
Abstract
Reactions of [Ru]Cl ([Ru] = Cp(PPh3)2Ru) with three alkynyl compounds 1, 5, and 8, each containing a cyclobutyl group, are explored. For 1, the reaction gives the vinylidene complex 2, with a cyclobutylidene group via a dehydration at CδH and CγOH. With an additional methylene group, 5 reacts with [Ru]Cl to afford the cyclic oxacarbene complex 6. The reaction proceeds via a vinylidene intermediate followed by an intra-molecular cyclization reaction by a nucleophilic addition of the hydroxyl group onto Cα of the vinylidene ligand. Deprotonation of 2 with NaOMe produces the acetylide complex 3 and alkylations of 3 by allyl iodide, methyl iodide and ethyl iodoacetate generate 4a-c, respectively, each with a stable cyclobutyl group. Dehydration of 1 is catalyzed by the cationic ruthenium acetonitrile complex at 70ºC to form the 1,3-enyne 7. Epoxidation reaction of the double bond of 7 yields the oxirane 8. Ring-expansion of the cyclobutyl group of 8 is readily induced by the acidic salt NH4PF6 to afford the 2-ethynyl substituted cyclopentanone 9. The same ring expansion is also seen in the reaction of [Ru]Cl with 8 in CH2Cl2 affording the vinylidene complex 10, also obtainable from 9 and [Ru]Cl. But, in MeOH, the same reaction of [Ru]Cl with 8 affords the bicyclic oxacarbene complex 12a via an additional cyclization reaction. Transformation of 10 to 12a is readily achieved in MeOH/HBF4, but, in MeOH alone, the acetylide complex 11 is produced from 10. In the absence of MeOH, cyclization of 10, induced by HBF4, is followed by a fluorination to afford complex 13. Crystal structures of 6 and 12a’ are determined by singel crystal diffraction analysis.
Subjects
ruthenium
carbene
cyclobutane
ring-expansion
oxirane
cyclization
Type
thesis
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