Facial selectivity in the nucleophilic additions of vinylmagnesium bromide to bicyclo[2.2.2]oct-5-en-2-one derivatives.
The levels of diastereoselection attainable by addition of vinylmagnesium bromide to a selection of bicyclo[2.2.2]octenone derivatives 1-6 in the presence of various Lewis acids such as LiBr, CeCl3, TiCl4, ZnBr2, MgBr2, and Et2AlCl have been determined. The 1,2-addition of ketone 1 with vinylmagnesium bromide in THF provided a mixture of anti- and syn-isomers. The reactions of 2 with vinylmagnesium bromide at room temperature afforded anti- and syn-isomers with preference to anti-isomers in most cases. These reactions in the presence of Lewis acids afforded anti-isomers as the major product with an excellent stereoselectivity or as single isomers in some cases. The ketones 3 gave surprisingly different results providing anti-isomers predominantly even in the presence of Lewis acids. The bicyclic ketones 4 and 5 and all-carbon tricyclic ketone 6 furnished the syn-isomer as the main product. There is no significant effect of Lewis acid catalysis in the nucleophilic addition reactions of 1, 4, 5, and 6. The use of a preformed vinylmagnesium bromide-CeCl3 reagent for the addition reactions of 2d-f and 3d-f provided almost exclusively syn-isomers. The substituents and reaction conditions can influence facial selectivity in the nucleophilic additions to the bicyclo[2.2.2]oct-5-en-2-one derivatives.
Juo
Wan-Jinq
WJ
Department of Chemistry, National Tsing Hua University, Hsinchu 300, Taiwan.
Lee
Tsung-Ho
TH
Liu
Wen-Cheng
WC
Ko
San
S
Chittimalla
Santhosh Kumar
SK
Rao
Chitneni Prasad
CP
Liao
Chun-Chen
CC
D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D007659:Ketones / Q000737:chemistry*; D008274:Magnesium / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism; D014753:Vinyl Compounds / Q000138:chemical synthesis* / Q000737:chemistry
D001643:Bridged Bicyclo Compounds; D007659:Ketones; D014753:Vinyl Compounds; D008274:Magnesium