Ethers with acyl halides

Lewis acids are also used in conjunction with acyl halides. The reagent Nal—BF3 etherate selectively cleaves ethers in the order benzylic ethers > alkyl methyl ethers > aryl methyl ethers. 

Because of the special structural requirements of the resin-bound substrate, this type of cleavage reaction lacks general applicability. Some of the few examples that have been reported are listed in Table 3.19. Lactones have also been obtained by acid-catalyzed lactonization of resin-bound 4-hydroxy or 3-oxiranyl carboxylic acids [399]. Treatment of polystyrene-bound cyclic acetals with Jones reagent also leads to the release of lactones into solution (Entry 5, Table 3.19). Resin-bound benzylic aryl or alkyl carbonates have been converted into esters by treatment with acyl halides and Lewis acids (Entry 6, Table 3.19). Similarly, alcohols bound to insoluble supports as benzyl ethers can be cleaved from the support and simultaneously converted into esters by treatment with acyl halides [400]. Esters have also been prepared by treatment of carboxylic acids with an excess of polystyrene-bound triazenes here, diazo-nium salts are released into solution, which serve to O-alkylate the acid (Entry 7, Table 3.19). This strategy can also be used to prepare sulfonates [401]. 

Silyl ethers of aliphatic alcohols are inert towards strong bases, oxidants (ozone [81], Dess-Martin periodinane [605], iodonium salts [610,611], sulfur trioxide-pyridine complex [398]), and weak acids (e.g., 1 mol/L HC02H in DCM [605]), but can be selectively cleaved by treatment with HF in pyridine or with TBAF (Table 3.32). Phenols can also be linked to insoluble supports as silyl ethers, but these are less stable than alkyl silyl ethers and can even be cleaved by treatment with acyl halides under basic reaction conditions [595], Silyl ether attachment has been successfully used for the solid-phase synthesis of oligosaccharides [600,601,612,613] and peptides [614]. 

Treatment of A and B with hydrogen over a nickel catalyst results in quantitative conversion of each compound to ferf-butyl alcohol. A reacts with acyl halides and anhydrides, whereas B is unaffected by these reagents. Treatment of 1 mole of A with excess methylmagnesium iodide in diethyl ether solution produces 1 mole of methane and 1 moie each of ferf-butyl alcohol and methanol. One mole of B with excess methylmagnesium iodide produces 1 mole of 2-methoxy-2-methylpropene and 1 mole of ferf-butyl alcohol. 

Under the influence of TiCU, acylation of a ketone via its enol silyl ether can be performed with acyl halides [2,3]- Acyl cyanides can also be used to acylate enol silyl ethers, as illustrated in Eq. (17) [83]. 

In related studies carried out by Gladysz and coworkers, the anionic silyl complex [(CO)4FeSiMe3] was found to react relatively cleanly with acyl halides, producing silyl enol ethers. The reaction with acetyl bromide gives a 70% yield of acetaldehyde trimethylsilyl enol ether (equation 89). An observed intermediate in this reaction was the... 

BIS(2-BUTOXYETHYL)ETHER (112-73-2) Combustible liquid (flash point 245°F/ 118°C oc). React violently with oxidizers, permanganates, peroxides, ammonium persulfate, bromine dioxide, sulfuric acid, nitric acid, perchloric acid, and other strong acids. Incompatible with acyl halides, aliphatic amines, alkalis, boranes, isocyanates. Flow or agitation of substance may generate electrostatic charges due to low conductivity. 

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