Aluminum oxide assisted stereoselective rearrangement of a cyclopropyl ketone to 4,5-dihydrofuran

Synthesis of substituted 3‐pyrrolidinecarbonitriles

“…In view of the synthesis of useful five-membered-ring heterocycles, cyclopropanes having at the same ring carbon by two electron-withdrawing groups are potential intermediates [1][2][3][4][5][6][7][8]. In previous papers we described a method leading to excellent yields of 1-acyl-2-oxo-3pyrrolidinecarbonitriles starting from N-acyl-1-cyanocyclopropanecarboxamides [9].…”

Mechanism of the decarboxylative rearrangement of α-(carbonyl)cyclopropane carboxylic acids to 2-substituted-4,5-dihydrofurans

“…A well documented chemistry of cyclopropyl rings adjacent to π systems is the ring opening of the cyclopropyl moiety and rearrangement to an extended cyclic system. This chemistry has been induced thermally 2 , photochemically 3 and with the use of catalysts 4 . Depending on the conditions, the mechanism of these reactions may range from formal ionic charges 5 , through diradical 6 to concerted 7 , ( [1,3] sigmatropic rearrangement).…”

“…While the rearrangement of vinylcyclopropanes to cyclopentenes 2,3 and cyclopropylimines to 4,5-dihydropyrroles 8 have found utility in synthesis, it is the rearrangement of cyclopropyl ketones to 4,5-dihydrofurans that has interested us 6c…”

“…The diradical mechanism was demonstrated through the regio-specificity of the ring expansion that lead to the dihydrofuran, the stereochemistry of the reaction lead to isomerization of stereochemical centers. This is a phenomenon of ring opening prior to ring closure is shared by the rearrangements of vinylcyclopropane and cyclopropylimines to the corresponding cyclopentenes and dihydropyrroles respectively 2,3,8 . It has been shown that the stereochemistry of the ring expansion could be controlled by the addition of Al 2 O 3 , which presumably acts as a template for the reaction 3 .…”

“…This is a phenomenon of ring opening prior to ring closure is shared by the rearrangements of vinylcyclopropane and cyclopropylimines to the corresponding cyclopentenes and dihydropyrroles respectively 2,3,8 . It has been shown that the stereochemistry of the ring expansion could be controlled by the addition of Al 2 O 3 , which presumably acts as a template for the reaction 3 . Another interesting reaction is the ring of opening cyclopropane carboxylic acid to the β,γ-unsaturated acid prior to decarboxylation 9 .…”