Acetolysis results for the various (3-methyl-substituted cyclopropyl tosylates are reported. The kinetic results are correlated with a treatment based on electronic and steric effects in ground and transition states, assuming stereospecific ring opening according to the Woodward-Hoffmann-DePuy predictions and considerable progress toward allyl cations in the transition states. The results of the standard mechanistic criteria [m value, (kRa ai J £ « ) , k0TjkBr, and a-methyl/hydrogen rate ratio] for the parent cyclopropyl system indicate that solvolysis is a concerted process. The magnitude of anchimeric assistance in the cyclopropyl system is estimated by two
1-Lithium-l-benzyloxy-butin-(2) (12) isomerisiert sich hauptsachlich zu l-o-Tolyl-butin-(2)-01-(I) (19), 1 -Lithium-1-[1 -phenyl-athoxy]-propen-(2) (13) in geringem AusmaR zu 1 -[o-Athylphenyl]-propen-(2)-01-(1) (20). Daneben bilden sich die Produkte 21 und 22 der Wittig-Umlagerung. Mechanistische Alternativen fur die ortho-Isomerisation werden diskutiert. -Bei der Wittig-Umlagerung von [9-Lithium-fluorenyl-(9)]-[butin-(2)-yl]-und -[pentin-(3)-yl-(2)]ather (26 bzw. 27) verschiebt sich der Alkinyl-Rest unter Propargyl-Allenyl-Isomerisierung.
I ,2-Migration to the Atom with free Electron Pair, VIII. ortho-Isomerization of Anionized Ethers and Mechanism of Migration of a Propargyl Group in the Wittig-rearrangement
1-Lithium-1-benzyloxy-but-2-yne (12) rearranges primarily to I -o-tolyl-but-2-ynol-(1) (19),1 -lithium-l-[l-phenyl-ethoxy]-2-propene (13) to a small extent to 1-o-ethyl-phenyl-2-propen-01-(I) (20). In addition the Wittig-rearrangement products 21 and 22 are formed. Mechanistic alternatives for the ortho-isomerisation are discussed. -For the Wittig-rearrangement of [9-lithium-fluorenyl-(9)]-[2-butynyl]-and -[3-pentynyl-(2)]-ether (26 and 27, respectively) the alkynyl group migrates with propargyl-allenyl-isomerisation.Wie seit Iangerem bekannt ist 21, konnen Ammonium-Ylide sowohl die Stevens-Umlagerung z-4) als auch die Sommelet-Umlagerung * , 5 . 6 ) (ortho-Umlagerung) eingehen.
Nach Wittig2) lagert sich Allyl-(9-lithium-fluoren-9-yl)-ather (im folgenden : [9-Lithium-fluorenyl-(9)]-allyl-ather)3) (1) bereitwillig zum Lithium-9-allyl-fluorenolat (6) urn.
Cyclobuten (I), Dichloxmethyläther (II) und Methyllithium/LiJ liefern das 3:2‐ Epimeren‐Gemisch aus den 5‐Methoxy‐bicyclo(2, 1 ,O)pentanen (III) und (IV).
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