Chiral compounds oxetanones

Chiral compounds (Continued) epoxy alcohols, 141 formulas, xiii xvii hydroxystannanes, 318 liquid crystals, 350 molecular lattics, 347 natural, 1 NMR spectra, 282 olefins, 173 oxetanones, 326 phenols, 287 see also Binaphthol phenylbutenes, 172 protonating agents, 324 sulfoxides, 159 sulfur ylides, 328 synthesis, I... 

Simple olefins do not usually add well to ketenes except to ketoketenes and halogenated ketenes. Mild Lewis acids as well as bases often increase the rate of the cyclo addition. The cycloaddition of ketenes to acetylenes yields cyclobutenones. The cycloaddition of ketenes to aldehydes and ketones yields oxetanones. The reaction can also be base-cataly2ed if the reactant contains electron-poor carbonyl bonds. Optically active bases lead to chiral lactones (41—43). The dimerization of the ketene itself is the main competing reaction. This process precludes the parent compound ketene from many [2 + 2] cyclo additions. Intramolecular cycloaddition reactions of ketenes are known and have been reviewed (7). 

The existence of ketenes was established over a hundred years ago, and, in recent years, asymmetric synthesis based on [2 + 2] cycloadditions of ketenes with carbonyl compounds to form chiral p-lactones has been achieved with high yields and high stereoselectivities. In 1994, Miyano et al. reported the use of Ca-symmetric bis(sulfonamides) as ligands of trialkylaluminum complexes to promote the asymmetric [2 + 2] cycloaddition of ketenes with aldehydes. The corresponding oxetanones were obtained in good yields and enantioselectivities... 

Danheiser and coworkers described a convenient preparation of oxetanones via the condensation of thioester lithium enolates with carbonyl compounds and subsequent lac-tonization under proper conditions592. The asymmetric version was reported later593, the configuration of the new chiral center being established by a stereospecific dyotropic rearrangement to the y-butyrolactone (Scheme 125)594. 

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