Lewis acidity effect

Boron trichloride, usually in conjunction with an additional Lewis acid, effects o-chloroacetylation of anilines. The resulting products are converted to indoles by reduction with NaBH4.[l], The strength of the Lewis acid required depends upon the substitution pattern on the ring. With ER substituents no additional... 

Lewis acid effects 435 1UPAC recommendations copolymer depiction 335 living polymerization 452 polymer structure 2... 

These reagents are appropriate even for very sensitive molecules. Their efficacy is presumably due to the Lewis acid effect of the aluminum and magnesium ions. The hindered nature of the amide bases also minimizes competition from nucleophilic ring opening. 

Bromides are less reactive than the corresponding iodides in atom transfer processes. However, activated bromides such as diethyl bromomalonate [36] and bromomalonitrile [53] react with olefins under Et3B/02 initiation. Kha-rasch type reactions of bromotrichloromethane with alkenes are also initiated by Et3B/02 [41]. On the other hand, a remarkable Lewis acid effect was reported by Porter. Atom-transfer reactions of an a-bromooxazolidinone amide with alkenes are strongly favored in the presence of Lewis acids such as Sc(0Tf)3 or Yb(0Tf)3, this reaction was successively applied to the... 

Lewis Acid Effects on Product Distributionf % Linear Nitrile Product... 

Lewis Acid Effects on Product Distribution Using Ni[P(0-p-toly[)3]t in 3pN ... 

Aluminium and copper Lewis acids effect a regioselective [l,3]-rearrangement of allyl vinyl ethers in moderate to good yields (Scheme 30). The use of trisubstituted alkenes leads to depressed levels of Claisen products.53... 

The detethering of one such trans cycloadduct (208), containing a tertiary ether linkage, was carried out. An El process, mediated by a Lewis acid, effected selective C-0 bond cleavage to give the most stable of the alternative regioisomeric carbo-cations, and finally olefin (209) (Scheme 54). 

The importance of 1,3-dipolar cycloadditions (1,3-DC) in the realm of heterocyclic synthesis is widely documented and recent results concerning the intramolecular version of this methodology, including reactions with nitrile oxides and nitrones for access to isoxazole derivatives, have been reviewed <07T12247>. A quantum chemical study of the Lewis acid effect on the cycloaddition of benzonitrile oxide to propyne has been reported evidencing a small influence on the outcome of the reaction <07T5251>. 

Titanium Lewis acids effect formal [2 + 2] cycloaddition as shown in Eqs (158) [401] and (159) [402,403]. Subtly changing the reaction conditions and substrates alters the product of Eq. (159) from the cyclobutane to a dihydrobenzofuran derivative, as will be described below. The analogous hetero [2 + 2] addition of a chiral aldehyde to a silylketene proceeded stereoselectively in the presence of titanium tetrachloride to give the propiolactone, as shown in Eq. (160) [404]. The silyl group was removed by the treatment with KF. 

Protonation of imines leads to improved yields in radical addition. For reviews of Lewis acid effects in radical reactions, see... 

The reaction of methyl stearolate (1) with diazoacetic ester in the presence of copper bronze produces a diester, which is hydrolyzed to the diacid (2). This is converted into the diacid chloride (3). Treatment with zinc chloride or other Lewis acid effects selective decarbonylation to give the cyclopropenium ion (4). Methanol is then added to convert the acid chloride grouping into the methyl ester (5). Finally reduction with sodium borohydride gives methyl sterculate (6). 

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