Ketones, 2-chloro homologation

As a sequel to the elegant and highly efficient synthesis of camphor by an intramolecular cyclization. Money et have successfully applied this method to the synthesis of the naturally-occurring sesquiterpenoids campherenone (110) and campherenol (111) whose structures and absolute stereochemistries have recently been deduced.In this sequence, dihydrocarvone (112) was readily converted into the keto-ketal (113) from which the homologated chloro-ketone (114) was obtained. Treatment of the corresponding enol acetate (115) with boron trifluoride in wet methylene chloride afforded the two bicyclic chloro-ketones (116) and (117) in 55-60% yield. Conversion of the corresponding iodo-ketals... 

Optically active a-chloro sulfoxides have recently been obtained by a very practical procedure using NBS and potassium carbonate with the expected inversion of configuration at sulfur. Chloro sulfoxides were shown to be very useful in the synthesis of epoxides and for a,3-unsaturated ketone homologation (Scheme 61b). ... 

Homologation of acids (esters). a-Chloro-a-phenylsulfinyl ketones are the condensation products of esters with chloromethyl phenyl sulfoxide. On treatment with t-BuLi-KH these ketones are converted to potassium alkynoxides, which can be transformed into acids through hydration. 

A convenient and high yielding carbonyl homologation involves the reaction of excess sodium phenylselenide with a phenyl-sulphinyl epoxide. The required epoxides are most easily prepared by the reaction of the anion of an a-chloro-sulphoxide with a ketone and ring closure of the resulting chlorohydrin with potassium hydroxide (equation 12). 

Reactive aldehydes can be homologated to a-chloro-a,/3-unsaturated ketones using diethyl trichloromethanephosphonate and the procedure exemplified in Scheme 51. ... 

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