Haller- Bauer cleavage

Short-lived chiral ion pairs are intermediates in the Haller-Bauer cleavage 14 15 of enantiomer-ically enriched 2,2-disubstituted 1,2-diphenylethanones, which give optically active phenylalka-nes on in situ protonation with partial retention of the configuration. 

Exercise 17-14 The Haller-Bauer cleavage of 2,2-dimethyl-1-phenyl-1-propanone with sodium amide forms benzenecarboxamide and 2-methylpropane. Write a mechanism for the Haller-Bauer reaction analogous to the haloform cleavage reaction. 

Method A Br-Li exchange, n-BuLi/Et20 followed by CO2 quench. Method B NaNH2 promoted Haller-Bauer cleavage of phenyl ketone. Method C LDA/THF, — 72°C, quench with Mel or MeOD. Method D H-D exchange vs. racemization using NaOMe. Method E LDA/Et20 at 25°C. Method F DNMR. 

It has been shown recently by Paquette and coworkers based on the earlier work of Walborsky and coworkers that under the conditions of a Haller-Bauer cleavage the optically active ketone 306 is transformed into the optically active trimethylsilyl species 307 with complete retention of configuration. 

Thus, under the reaction conditions the intermediate a-trimethylsilyl anion is configurationally stable. One should also mention that the Haller-Bauer cleavage proceeds with complete retention of configuration when Me, and possibly F and... 

Haller-Bauer cleavage of (— )-(R)-1 -benzoyl-1 -methyl-2,2-diphenylcyclopropane (5) by sodium amide in toluene produces (-f )-(S)-2-methyl-l,l-diphenylcyclopropane (2) with retention of configuration. ... 

Haller-Bauer cleavage. 2-Benroyl-2-phenylbicyclo[l.l.l]pentane (1) is cleaved to 2-phenylbicyclo[l.l.l]pentane (2) by sodium amide in refluxing benzene.The product can be converted into the carboxylic acid 3. 

Other references related to the Haller-Bauer cleavage are cited in the literature... 

The quasi-Favorskii rearrangement has been used often in the synthesis of unnatural, conplex, polycyclic structures. Indeed, this method is uniquely suited for such targets. However, undesired side reactions can occur. An exanple, discussed here within its mechanistic context, is based on a report by Ueda and coworkers. They treated the polycyclic dibrominated diketone 37 with potassium hydroxide in the expectation of obtaining cubane-l,3-dicarboiq lic acid 38. Given what was known about quasi-Favorskii reactions at the time (vide supra), the plan made perfect sense. However, exposure of 37 to 5% KOH for 15 min at 80 °C afforded not 38 but the cyclopropyl lactone 43 fScheme 7.12). A proposed mechanism for the process began with a Haller-Bauer cleavage, always a potential risk in quasi-Favorskii... 

THF containing a small amount of water has also been found to effect oxidation followed by Haller-Bauer cleavage to give 2-carboxybiphenyl [19]. 

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