Reactions migrations, chloro group

Whereas diaryl ditellurium compounds and copper powder in refluxing dioxane yielded diaryl tellurium derivatives (p. 419), bis[3-chloro-2-acyloxypropyl] ditellurium compounds lost both tellurium atoms under these conditions. The tellurium-free products were propenes. During the reaction the acyloxy group migrated to take the place of the chlorine atom5. 

Reaction of the preformed PdCl -nOrbomadiene jt-complex vvith diphenylmercury or sodium tetraphenylborate produces the endo-phenyl endo-norbornenylpalladium complex . The mercurial or borate apparently exchange a phenyl for a chloro group and the phenyl migrates to one of the double-bond carbons. The second double bond remains coordinated to the metal during the reaction ... 

Nucleophilic Substitution, Metallation, and Halogen-Metal Exchange.—Direct nucleophilic displacement of the 7-chloro-group of 7-chloro-3-methyl-benzo[b]thiophen has been achieved. 3-Bromobenzo[b]thiophen was reduced to the 3-deuterio-derivative by the reaction with sodium borodeuteride and palladium chloride. Meisenheimer complexes were formed in the reaction of methoxide ion with 2-methoxy-3-nitro- and 3-methoxy-2-nitrobenzo[b]thiophen. Rate and equilibrium data were determined in methanol at 25 C. On treatment of 2-bromobenzo[b]thiophen with potassium amide in liquid ammonia, bromine migration to the adjacent carbon atom was observed. Considerable evidence for the occurrence of an intermolecular transbromination was obtained. The reaction of 3-bromo-benzo[b]thiophen with piperidine has been reinvestigated and found to give primarily the normal, but also some of the cine-substitution product, which is the only product obtained in the reaction of 2-bromobenzo[b]thiophen. Possible mechanisms for some of these reacticms are suggested. 

The reaction of silylborane with 1-halo-l-lithio-l-alkenes yields 1-boryl-l-silyl-l-alkenes via borate formation followed by 1,2-migration of silyl group (Equation (90)).76,240 The mechanism seems to be closely related to that proposed for the silaboration of isocyanide (Figure 2). Vinyl-substituted carbenoids, l-chloro-l-lithio-2-alkenes, react with silylpinacolborane to give l-boryl-l-silyl-2-alkanes in good yield (Equation (91)).241 This methodology is applied to the synthesis of l-boryl-l-silyl-2-cyclobutene.2 2 Similar reactions are carried out with other carbenoid... 

If the pKa of the corresponding acid R1 - H from the stabilized carbanion is smaller than 35, the migration of R1 fails in (dichloromethyl)borate complexes. Failure to convert pinanediol [(phenylthio)methyl]boronate to an a-chloro boronic ester has been reported15. Reaction of (dichloromethyl)lithium with an acetylenic boronic ester resulted in loss of the acetylenic group to form the (dichloromethyl)boronate, and various attempts to react (dichloromethyl)boronic esters with lithium enolates have failed17. Dissociation of the carbanion is suspected as the cause, but in most cases the products have not been rigorously identified. 

Syntheses of simple diols are described first, followed by a multistep synthesis of ribose. These syntheses illustrate the compatibility of alkoxy substituents on boronic esters with their reaction with (dihalomethyl)lithium. The limitations of this compatibility, as well as failure of a (chloro-allyl)boronic ester to undergo substitution by alkoxides, are also noted. Retention of configuration of the migrating group is a consistent and repeated feature of these syntheses. 

Migration of tertiary alkyl groups in the dichloromethyl methyl ether reaction does however mean that ketones cannot be synthesized using thexylborane and the approach adopted in the carbonylation and cyanidation processes. In order to obtain ketones by this route, boranes bearing chloro or alkoxy groups, i.e. groups of very low migratory aptitude, have to be used as substrates (Equation B3.17). 

Nakayama and Tanaka found that the chlorination of 2-silylfuran 109 with sulfuryl chloride gave the corresponding 2-chloro-3-silylfuran 110 and 2-chlorofuran 111 as shown in equation 75184. 1,2-Migration of a pentacoordinate silicate group was assumed to be involved in this reaction (equation 76). 

The reaction of tellurium tetrachloride with 3-acyloxypropenes in chloroform takes a course different than the reaction with propene. The products obtained from 3-acyloxypropenes are l-chloro-2-acyloxy-3-propyl tellurium trichlorides. These reactions proceed via syn-addition of tellurium tetrachloride with concomitant migration of the acyloxy group to the middle carbon of the propene7. 

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