Benzaldehyde → 2-Benzoylbenzaldehyde

Beteiligte Stoffe

Reaktionsschritte

The benzaldehyde of formula VII may be prepared from the corresponding methyl-substituted benzophenone. The methyl substituent is first subjected to side-chain bromination, e.g. by treatment with bromine and the resulting dibromomethyl benzophenone hydrolysed with strong mineral acid, e.g. sulphuric acid to give the corresponding benzoyl-benzaldehyde. The aldehyde group can then be protected, e.g. as an acetal or ketal and the unprotected carbonyl group linking the two aromatic rings then reacted with methyl magnesium iodide under the conditions of the Grignard synthesis followed by dehydration or reacted with a Wittig reagent to convert that carbonyl group into a corresponding 1-phenylvinyl benzaldehyde in which the aldehyde group is protected. The protecting group can then be removed to give the 1-phenylvinyl benzaldehyde which can then be reacted with methyl magnesium iodide, hydrogen cyanide or ethynyl magnesium bromide to give the correspondingly α-substituted 1-phenylvinyl benzyl alcohol. Protection of the aldehyde group is not necessary when, for example, an α-methyl-benzyl alcohol product is required. In such a case, a benzoyl-benzaldehyde can be reacted with 2 equivalents of, for example, methyl magnesium iodide in accordance with the reaction: ##STR13## The Grignard technique can also be used directly on α-substituted benzoyl-benzoyl alcohols, e.g. in accordance with the reaction: ##STR14##

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