Mozingo method

If the alkyne contains an alcohol group, this may attack the ketene intermediate leading to a lactone after oxidative removal of the chromium (Scheme 8.28). This reaction has been used in syntheses of blast-mycinone 8.106 and antimycinone 8.107, starting from a protected lactaldehyde 8.102, and employing the Mozingo method at the end to remove the undesired keto group from the ketene cyclization product 8.105 (Scheme 8.29) ... 

A modification of the K-R reaction was introduced by Mozingo. This method involved reacting an o-hydroxyacetophenone with an ester in the presence of metallic sodium to form a 1,3-diketone. Treatment of the diketone with an acid then delivered the chromone via an intramolecular cyclization reaction. This method was applied to the preparation of 2-ethylchromone (21). 0-hydroxyarylketone 22 was allowed to react with ethyl propionate (23) in the presence of sodium metal.The resulting sodium enolate was then quenched with acetic acid to deliver the 1,3-diketone 24. Upon heating 24 in glacial acetic acid and hydrochloric acid, 2-ethylchromone (21) was delivered in 70-75% overall yield. 

Method 1 is a new method for the direct production of flavone from o-benzoyloxyacetophenone and has been successfully applied to the synthesis of other flavones. Method 2, which involves the Baker-Venkataraman transformation, is recommended because of its high over-all yield and the reproducibility of the results. Mozingo and Adkins method 8 is satisfactory but the yield of 0-hydroxydibenzoylmethane is variable. 

Raney nickel catalyst can be prepared by the method of Mozingo.3 The submitters used Raney nickel catalyst obtained commercially from the Gilman Paint and Varnish Company,... 

Reduction of carbonyl group to methylene via thioacetals In contrast to the Clemmensen reduction (section 6.4.3) and Wolff-Kishner reduction (section 6.4.4), this method does avoid treatment with strong acid or base but requires two separate steps. The first step is to convert the aldehyde or ketone into a thioacetal. The second step involves refluxing an acetone solution of the thioacetal over a Raney nickel. This reduction method is known as Mozingo reduction. Hydrazine can also be used in the second step. 

Thioacetals are useful because they undergo desulfurisation when treated with Raney nickel in the Mozingo reduction. This is an excellent method for reducing aldehydes or ketones to alkanes. 

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