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An allylic rearrangement or allylic shift is an organic reaction in which the double bond in an allyl chemical compound shifts to the next carbon atom. It is encountered in nucleophilic substitution. In reaction conditions that favor a SN1 reaction mechanism the intermediate is a carbocation for which several resonance structures are possible. This explains the product distribution (or product spread) after recombination with nucleophile Y. This type of process is called an SN1' substitution. Alternatively, it is possible for nucleophile to attack directly at the allylic position, displacing the leaving group in a single step, in a process referred to as SN2' substitution. This is likely in cases when the allyl compound is unhindered, and a strong nucleophile is used. The products will be similar to those seen with SN1' substitution. Thus reaction of 1-chloro-2-butene with sodium hydroxide gives a mixture of 2-buten-1-ol and 1-buten-3-ol: : Nevertheless, the product in which the OH group is on the primary atom is minor. In the substitution of 1-chloro-3-methyl-2-butene, the tertiary 2-methyl-3-buten-2-ol is produced in a yield of 85%, while that for the primary 3-methyl-2-buten-1-ol is 15%. In one reaction mechanism the nucleophile attacks not directly at the electrophilic site but in a conjugate addition over the double bond: : ==Scope== The synthetic utility can be extended to substitutions over butadiene bonds:〔''Molecular yardsticks. Synthesis of extended equilibrium transfer alkylating cross-link reagents and their use in the formation of macrocycles''Stephen J. Brocchini, Martin Eberle, and Richard G. Lawton J. Am. Chem. Soc.; 1988; 110(15) pp 5211 - 5212; 〕 : :''Reaction in methanol and catalyst diisopropylethylamine'' In the first step of this macrocyclization the thiol group in one end of ''1,5-pentanedithiol'' reacts with the butadiene tail in 1 to the enone 2 in an allylic shift with a sulfone leaving group which reacts further with the other end in a conjugate addition reaction. In one study〔''Double Lawton SN2'Addition to Epoxyvinyl Sulfones: Selective Construction of the Stereotetrads of Aplyronine'' A Ahmad El-Awa and Philip Fuchs Org. Lett.; 2006; 8(14) pp 2905 - 2908; (Letter) 〕 the allylic shift was applied twice in a ring system: : In this reaction sequence a Jacobson epoxidation adds an epoxy group to a diene which serves as the leaving group in reaction with the pyrazole nucleophile. The second nucleophile is methylmagnesium bromide expulsing the pyrazole group. An SN2' reaction should explain the outcome of the reaction of an aziridine carrying a methylene bromide group with methyllithium:〔''Highly unusual conversion of 1-alkyl-2-(bromomethyl)aziridines into 1-alkyl-2-(N-alkyl-N-ethylaminomethyl)aziridines using methyllithium'' Matthias D'hooghe and Norbert De Kimpe Chem. Commun., 2007, 1275 - 1277, 〕 : In this reaction one equivalent of acetylene is lost. Examples of allylic shifts: *Ferrier rearrangement *Meyer–Schuster rearrangement 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Allylic rearrangement」の詳細全文を読む スポンサード リンク
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