Birch reduction scope

Companion reactions that serve to expand the scope of the asymmetric Birch reduction-alkylation strategy... 

The normal Birch reduction is most interesting when applied to aromatic ethers 209 or acids 213. The addition of two electrons may make a dianion in which the charges keep away from the ether 210 but conjugate with the acid 214. Protonation of 210 gives the enol ether 211 and hence the non-conjugated enone 212. The dianion 214 has a proton which transfers to the less stable anion leaving the enolate 215 that can be alkylated to give 216. None of these compounds is chiral and there appears to be little scope for asymmetric induction. 

A better route is the one shown in Scheme 11. The benzene complex 104 forms readily in near quantitative yield upon heating Ru(III) chloride and 1,3-or 1,4-cyclohexadiene in EtOH. The introduction of the Cp ligand is by hali-de/Mcp exchange. The classic procedure to 105 required a stoichiometric quantity of thallium or silver [103], but a very recent, improved procedure shows that cyclopentadiene/K2C03/ abs. EtOH can be used successfully [104]. Although beyond the scope of this review, it is interesting to note that the much less electrophilic complexes [(arene)Ru(C5Me5)] [PFg] are accessible in a one-pot procedure from RuClj [105]. The sequence Birch reduction/complexa-... 

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