Cyclobutanones synthesis

Ketene acetals and thioacetals can be used as ketene equivalents in cyclobutanone synthesis in situations where ketene to alkene cycloadditions are inefficient such as in the case of electron-deficient alkenes.14 Although thermal cycloadditions of ketene acetals and thioacetals with electron-deficient alkenes have been observed (see Section 1,3.2.1.), such cycloadditions proceed more efficiently and under milder conditions with metal catalysts. Efficient cycloadditions between ketene dimethyl acetal and alkenes substituted by a single electron-withdrawing group have been reported.15... 

Trost developed a general method of synthesis of vinylcyclqnopanes (and their sulfur and oxygen analogs) through the application of ylide addition to carbmyl compounds. Three major methods involve the cyclopentene annulation, cyclobutanone synthesis, and ring expansion with concomitant alkylation (Scheme 51). °... 

Regio problems can arise if aromatic ketones are involved in the cyclobutanone synthesis, and aldehydes can only be forged into the cyclobutanone skeleton by detouring via methylthio-substituted cyclopropanes (equation 130) ... 

Cyclobutanediol, 1,2-dimethyl- synthesis, 53 Cyclobutanone, 2-hydroxy- synthesis, 54 Cyclobutanones synthesis, 77, 79, 335-336 Cyclobutene synthesis, 142... 

Cyclobutauones. Trost s original cyclobutanone synthesis (4, 211-214 definitive papers ) by rearrangement of oxaspiropentanes with lithium salts results in selective formation of the cyclobutanone in which the new carbon to carbonyl bond is introduced on the more sterically hindered face of the ketone. He and Scudder have now found that the isomeric cyclobutanone becomes the predominant product if the oxaspiropentane is rearranged through a selenoxide. An example is the rearrangement of 1. When lithium perchlorate is used the cyclobutanone 2 is obtained. On treatment with sodium selenophenolate followed by oxidation, the cyclobutanone 4 becomes the major product. In some cases this new selenoxide route is stereospecific and results in essentially only one cyclobutanone. 

Miscellaneous.—a-Elimination. Further examples of cyclobutanone synthesis employing lithium diphenylsulphonium cyclopropylide have been reported. ... 

The [2 + 2] process for cyclobutanone synthesis is a companion path in the insertion (acylpalladation) process. The utility has been demonstrated in j8-lactam synthesis. 

Miscellaneous.—OrElimination. Lithium diphenylsulphonium cyclopropylide continues to be used in cyclobutanone synthesis, and a more efficient rearrangement of the initially produced spiro-epoxide is achieved by the use of lithium tetrafluoro-borate. A promising alternative route to cyclobutanones is shown in Scheme 64,... 

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