Cooperation of Cis Vicinal Acceptors for Donor-Acceptor Cyclopropane Activation: TfOH-Promoted Ring-Opening/Aryl Shift Rearrangement to 3- And 5-Ylidenebutenolides
A convenient route to 3- and 5-ylidenebutenolides from readily available cis-2-acylcyclopropane-1-carboxylates is described. Upon exposure to TfOH, synergistic activation of the vicinal acceptors in cis-2-acylcyclopropane-1-carboxylates generates highly strained bicyclic oxocarbenium ion intermediates, which undergo the ring-opening/aryl shift/deprotonation cascade process to form the 3- or 5-ylidenebutenolides depending on the acyl group. On the other hand, the corresponding trans isomers, from which it is difficult to form such oxocarbenium ions, are inactive under the same conditions.
Shao, Jiru,Luo, Qinyuan,Bi, Hongyan,Wang, Sunewang R.
Efficient and Flexible Syntheses of Paraconic Esters and Other Highly Substituted Furanone Derivatives from Methyl 2-Siloxycyclopropanecarboxylates
Deprotonation of methyl 2-siloxycyclopropanecarboxylates 1 with lithium diisopropylamide and reaction of the resulting enolates with carbonyl compounds produce trifunctional cyclopropane derivatives.These primary adducts can only be isolated with good yie
Brueckner, Christiane,Reissig, Hans-Ulrich
p. 2440 - 2450
(2007/10/02)
C-C-Bond Formation by Lewis Acid Induced Cyclopropane Ring Cleavage - New Routes to Highly Substituted Furan(one) Derivatives
Activation by stoichiometric quantities of titanium tetrachloride allows addition of ketones to methyl 2-siloxycyclopropanecarboxylates 1, which affords hydroxylalkylation products 3/4 under ring cleavage.There are, however, restrictions regarding the cyc