Ethers, cyclic cleavage with

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]. 

Tee ZnCl2 acts as a Lewis acid and can be used either to remove chloride from MeCOCl or to cuenplex with its carbonyl oxygen atom, in either case making it a better electrophile so that it can ck the unreactive oxygen atom of the cyclic ether. Ring cleavage by chloride follows. 

Scheme 16.14 shows the reactions of two dimeric cyclic ether lignin models with O2 [64] Oxidation of the dimeric cyclic ether pinoresinol, 54 with O2 from NaOCl/ H2O2 at pH 7 underwent cleavage of the phenyl-aliphatic bond to produce meth-oxy-hydroquinone, 50 and 2,6-dihydroxy-3,7-dioxabicyclo [3.3.0] octane, 55. When treated under the same conditions as pinoresinol, 54, dihydrodehydrodiisoeugenol, 56 did not undergo any bond cleavage but rather an oxidation of the phenolic moiety to form the quinol, 57 (Scheme 16.14). 

Ninomiya (A + B)0 - ->c4- Dio Sacrificial rings cleaved in step 8 (epoxide to ketone transformation catalyzed by BF3 etherate), step 14 (oxidative cleavage of cyclic diol with NaI04)... 

The ability of perfluorinated ethers to react with anhydrous AICI3 at elevated temperatures was discovered by Tiers. While the reaction of alicychc perfluorinated ethers results in the cleavage with the formation of acyl chloride and chloro-fluoroalkanes, perfluorinated a-aUcyl tetrahydrofuranes undergo replacement of all three a-fluorines with the formation of cyclic a,a,a-trichloro derivatives. Later, this reaction was extensively studied by Abe (Fig. 9... 

Trimethylsilyldiethylamine as Halosilane Equivalent. Tri-methylsilyldiethylamine has recently found applications in preparation (in situ) of difficult-to-handle and highly moisture-sensitive iodosilanes and bromosilanes. This method has been used for a variety of synthetic transformations, including cleavage of cyclic ethers, cyclic acetals, and oxazolidines. The conversion of esters to carboxylic acids may also be accomplished with trimethylsi-lyldiethylamine as shown in the following examples. It may be suggested that other reactions of iodosilane and bromosilane can be carried out by means of trimethylsilyldiethylamine. 

The reductive cleavage of -bromo ethers is a related reaction. If the ether is cyclic, the reverse reaction takes place on treatment with NBS ... 

---