Oxy-cope rearrangements of bicyclo[3.2.0]heptenones. Synthesis of bicyclo[4.2.1]non-1(4)-en-6-ones and bicyclo[5.2. 1]dec-1(10)-en-5-ones.
6-exo-Methylbicyclo[3.2.0]hepten-7-ones and their 2-alkylidene analogues are readily prepared from dialkyl squarates. These compounds undergo facial oxy-Cope ring expansions upon treatment with vinyllithium; the former leads to bicyclo[4.2. 1]non-1(4)-en-6-ones and the latter to the first examples of bicyclo[5.2.1]dec-1(10)-en-5-ones, compounds having exceptionally strained bridgehead double bonds. The transformations are controlled by the 6-exo-methyl group in the starting material along with the substituent at position-1 (bridgehead) which force attack of the lithium reagent from the concave face of the starting material, thus allowing the cyclopentenyl or alkylidene groups to participate in the sigmatropic event.
Verma
S K
SK
Department of Chemistry, University of California, Irvine, California 92697-2025, USA.
Nguyen
Q H
QH
MacDougall
J M
JM
Fleischer
E B
EB
Moore
H W
HW
D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis*; D007202:Indicators and Reagents; D007659:Ketones / Q000138:chemical synthesis*; D009682:Magnetic Resonance Spectroscopy; D017646:Organosilicon Compounds / Q000737:chemistry
D001643:Bridged Bicyclo Compounds; D007202:Indicators and Reagents; D007659:Ketones; D017646:Organosilicon Compounds; C404749:tert-butyldimethylsilyl chloride