Displacement from carboxylate, carbamate and cyanate

The usual reactions of organomagnesium compounds with esters, amides and nitriles are those described in Sections 5.3, 6.2 and 6.3. However, factors such as steric hindrance and stability of leaving group may lead to reactions resulting in overall nucleophilic displacement. Most of them are of limited applicability (see Ref. [39] for examples involving carbamate), but two warrant coverage. 

Catalysed reactions of organomagnesium compounds with allylic acetates are potentially useful in synthesis, but lack of regioselectivity may be a problem  

However, a systematic study has demonstrated that the regiochemistry can be controlled [40] conditions favouring dialkylcuprate as the catalytic intermediate (fast addition of Grignard reagent), low temperature, low concentration of catalyst), favour a-attack, leading to (1), whereas conditions favouring formation of alkylcopper (slow addition of Grignard 

Yields are variable, but in favourable cases can be very high for example, phenyl cyanate and t-butylmagnesium chloride gave pivalonitrile (92%) and phenol (87%). 

---