Arenes aryl carbamates

The role of aggregates and mixed aggregates on the lithium diisopropylamide-mediated anionic Fries rearrangements of aryl carbamates (Scheme 7) has been described.57 Substituents at the meta -position of the arene (X = H, OMe, F) and the... 

Two recent computational studies have examined the mechanism of crosscouplings involving aryl acetates, earbamates, and sulfamates. In a study of synthetic advances with aryl pivalates, oxidative addition of Ni(0) to the aryl acetate was found to proceed by a three-centered mechanism via an T arene complex. Alternatively, in a separate study, oxidative addition involving aryl carbamates and sulfamates was found to proceed by a five-centered transition state, with coordination of the carbonyl oxygen to nickel being a key interaction in the oxidative addition. ... 

Directed orf/to-metalation (DoM) chemistry [81] further reinforces the versatility of nickel-catalyzed C-O bond activation reactions. Based on the strong accelerating and orf/to-directing effect of carbamate functionality in the base-induced deprotonation of arenes, an array of electrophiles can be introduced at the ortho position of aryl carbamates. For instance, DoM of dicarbamate, followed by 1,2-addition to a,(3-unsaturated aldehyde and intramolecular cyclization, furnishes the 2//-chromene derivative (Scheme 8) [82]. The carbamate director can finally be arylated under a nickel-catalyzed Suzuki-Miyaura-type reaction [47]. 

The CDC of 0-phenyl carbamates with arenes using Na S O in place of was described in 2011 (Scheme 24.25) [26]. The scope and selectivity of these arylations are similar to those described for transformations in Scheme 24.24. Preliminary studies were conducted to gain insight into the mechanism of the undirected C—H activation (step ii, pathway A, Scheme 24.19). A competition reaction of 26 with an equimolar amount of C H and 1,2-dichlorobenzene leads to biaryl 26a in 90% yield (Scheme 24.26). These results suggest that electron-rich arenes undergo aryla-tion at a faster rate than electron-neutral arenes. The authors propose an electrophilic aromatic... 

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