Intramolecular reactions Brook rearrangement

These reactions are thought to proceed by initial formation of the lithio propargylic alcohol adduct, which undergoes a reversible Brook rearrangement (Eq. 9.14). The resulting propargyllithium species can equilibrate with the allenyl isomer and subsequent reaction with the alkyl iodide electrophile takes place at the allenic site. An intramolecular version of this alkylation reaction leads to cyclic allenylidene products (Eq. 9.15). 

Benzyl and allylsilanes 87 and 89 can be formed by reductive lithiation and [l,4]-retro-Brook rearrangement of benzyl and allylsulfides 86 and 88 containing silyl ethers.63 The reaction, by virtue of the intermediacy of a configurationally unstable benzyl or allyllithium, is stereoselective but not stereospecific. In the latter case, intramolecularity assures the regioselective formation of 89. 

Intramolecular cyclisation of allgmyl a-ketoanilides (8) utilising the [l,2]-phospha-Brook rearrangement catalysed by a phosphazene base (12) has been developed by Terada and co-workers. Reactions involved a... 

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