The only drawback is the requirement of at least two equivalents of Grignard .
This can partly be circumvented by the use of a dual Grignard system with a cheap reducing Grignard such as n - butylmagnesium bromide .
The only drawback is the requirement of at least two equivalents of Grignard although this can partly be circumvented by the use of a dual Grignard system with a cheap reducing Grignard such as n - butylmagnesium bromide .