Cleavage regiospecific

Since the formation of silyl enol ethers from the corresponding ketones is subject to dther thermodynamic or kinetic control, Ais reagent can be used (as demonstrated in equation 36) to achieve useful regiospecific cleavages. 

PotassiumI biphenyl Regiospecific cleavage of alkyl aryl ethers... 

An important stage in the synthesis has been reached. It was anticipated that cleavage of the trimethylsilyl enol ether in 18 using the procedure of Binkley and Heathcock18 would regiospecifically furnish the thermodynamic (more substituted) cyclopentanone enolate, a nucleophilic species that could then be alkylated with iodo-diyne 17. To secure what is to become the trans CD ring junction of the steroid nucleus, the diastereoisomer in which the vinyl and methyl substituents have a cis relationship must be formed. In the... 

Recent work has shown that there are many assumptions required in order to use the silane-cleavage method. However, an advantage of this approach is that it can be nsed to determine acidities at regiospecific positions in very weak acids, including those for which the conjugate base anion is unstable with respect to electron detachment. 

The radical-induced cleavage of a,/ -aziridino alcohols proceeds in analogy to that of a,/ -epoxyalcohols, leading regiospecifically to allyl amines (a). By successive reactions with double bond systems, pyrrolidines are formed (b) [68]... 

Table 6.6. Substrate Regiospecificity of Selected Peptidases toward Some Peptides Containing only Common Amino Acids only Main Site(s) of Cleavage Are Indicated. See text for further details and additional references [139][143 - 155]. 

Sauers and coworkers have applied the Paterno-Biichi reaction to engeneral formula 427 (Scheme XXXIV) Reductive cleavage of these products with lithium aluminium hydride is also regioselective and leads, following oxidation, to ketones... 

An elegant, general synthetic route to spirocarbocyclic systems (cf. Vol. 5, p. 55) involving regiospecific ring cleavage of appropriate tricyclic ketones [c/. (83)- (84)]... 

Another example is the indirect acetonylation of a 1,2,3,4-tetrahydropyridine derivative at the (3-position of the enamide system [99]. The reaction involves a double alkylation to furnish an acetylcyclopropane which undergoes fragmentation on acid treatment. It is noted that polarity alternation and ring strain relief allow the facile and regiospecific C-C bond cleavage to proceed, the intervention of a cyclopropane intermediate also leads to disjoint system. This is a fundamental strategy [100] which has been frequently employed to gain access to compounds with disjoint functionalities. 

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