ipso Nitration. XXIII. Reactions of cyclohexadiene adducts from nitration of 4-ethyltoluene in acetic anhydride

Abstract

. Can. J. Chem. 59,2314Chem. 59, (1981. The diastereoisomers of 4-ethyl-1-methyl-4-nitrocyclohexa-2,s-dienyl acetate (1) and 1-ethyl-4-methyl-4-nitrocyclohexa-2,sdienyl acetate (2) are stereospecifically reduced to the corresponding nitrocyclohexadienols with aluminum hydride. Each dienol is stereospecifically methylated to the corresponding methyl ether with methyl iodide, silver oxide, and potassium hydroxide. Acid-catalysed solvolysis of the acetates 1 and 2 results in the substitution of the acetate moiety by other nucleophiles and these reactions are not stereospecific. The products of rearomatization of dienyl acetates, dienols, and dienyl methyl ethers depend on the acidity and ionizing power of the solvents and are readily explained in terms of reactions involving a nitrocyclohexadienyl cation or acetoxy-(hydroxy-, methoxy-)cyclohexadienyl cation as key intermediates. In the 4-acetoxy-4-alkylcyclohexadienyl cation 1,2-migration of the acetoxyl group is more rapid than alkyl migration, but 1,2-alkyl migration is faster than migration ofthe hydroxyl or methoxyl groups in the corresponding cations. l-Ethyl-4-methoxy-4-methylcyclohexa-2,S-dien-l-ol and 4-ethyl-3-nitrotoluene are significant minor products in the solvolysis of l-ethyl-4-methyl-4-nitrocyclohexa-2,5-dien-l-ol in aqueous methanol. Nitration of p-ethyltoluene in the presence of sulfuric acid or in trifluoroacetic anhydride gives a mixture of 4-ethyl-2-nitro-and 4-ethyl-3-nitrotoluene in a 2: 1 ratio. on peut facilement expliquer la formation de divers produits sur la base de reactions impliquant, comme intermediaire cle, soit un cation nitrocyclohexadienyle ou un cation acCtoxy (hydroxy ou mtthoxy) cyclohexadiCnyle. Dans le cation acetoxy-4 alkyl-4 cyclohexadienyle, la migration-1,2 du groupe acetoxy est plus rapide que la migration alkyle, mais la migration-1,2 des groupes alkyles est plus rapide que la migration correspondante des groupes hydroxyle ou methoxyle. L'ethyl-1 mCthoxy-4 methyl-4 cyclohexadikne-2,s 01-1 et I'ethyl-4 nitro-3 tolukne sont des produits secondaires importants de la solvolyse de I'kthyl-1 methyl-4 nitro-4 cyclohexadiene-2,s 01-1 dans le methanol aqueux. La nitration du p-Cthyltoluene en presence d'acide sulfurique ou dans I

Efficient Total Synthesis of Racemic Bisabolane Sesquiterpenes Curcuphenol and Xanthorrhizol Starting from Substituted Acetophenones

“…2.2.1 Preparation of Acetophenone 5. Since acetophenone 5 is not commercially available, we decided to develop an alternative approach to that already reported [19] for the synthesis of 5, which resulted in an economical and efficient starting material for the total synthesis of xanthorrhizol (2). Actually, compound 5 is a natural product isolated from the red seaweed Laurencia chilensis, which exhibits moderate antimicrobial activity [20].…”

ipso Nitration. XXVII. The crystal structure and stereochemistry of 3-bromo-6-methyl-6-nitrocyclohexa-2,4-dienyl acetate, 5-bromo-2-methyl-6-nitrocyclohexa-2,4-dienyl acetate, and 3-bromo-6-methyl-6-nitrocyclohexa-2,4-dienyl chloride

“…Generally the formation of adducts is under kinetic control (19) as is evident in the present instance from the fact that in the thermal rearrangement, when equilibrium conditions are approached, both diastereomers l a and l b are present together. Thus we must look to the transition state to account for the stereoselectivity.…”

“…-z ; (2 + x), (4 -y), (a + z); and (2 -x), (2 + y), (2 -z ) . The cell dimensions were refined by least squares using pairs (19,13, and 8, respectively) of 28 measurements obtained by an automatic centering routine. The asymmetric unit was one molecule in each case.…”

ipso Nitration. XXVIII. Nitration of 4-substituted toluenes: 1,2 adducts

“…It is known that formation of the adduct is subject to kinetic control (30) and thus it is the energetics of the transition states for trapping of the ipso cation that determine the preferred adduct. It is plausible that the greater formation of 1 , 2 adduct in the case ofp-tert-butyltoluene is the consequence of a steric effect since in the series of 4-alkyltoluenes (alkyl = Me, Et, i-Pr, t-Bu) it is only in the last case that 1,2 adduct is obtained and the alkyl groups should have very similar electronic effects, but markedly different steric effects.…”