Radical 1,2‐O→C Transposition for Conversion of Phenols into Benzoates by O‐Neophyl Rearrangement/Fragmentation Cascade

Metal‐Free Transformation of Phenols into Substituted Benzamides: A Highly Selective Radical 1,2‐O→C Transposition in O‐Aryl‐N‐phenylthiocarbamates

“…The first calculated energy profile for this process presented in Figure 2 illustrates that this reaction should be significantly slower than the O-and N-neophyl rearrangement in this system. Similar to the previous DFT calculations performed on the rearrangement of diaryl thiocarbonates, [3] our computational analysis at the UB3LYP/6-31 + G** level on thiocarbamates suggests a concerted mechanism for the O-neophyl rearrangement/fragmentation pathway. This observation contrasts with earlier computational [2,12] and experimental [13] support for a stepwise mechanism with the formation of a three-membered radical intermediate in systems where the O-neophyl rearrangement step is not coupled with fragmentation.…”

“…(1)]), [2] our lab has re-cently developed a convenient procedure for the conversion of phenols into benzoate esters. [3] This transformation was designed through rerouting the reaction via an O-neophyl rearrangement [5] /fragmentation sequence (Scheme 1,A C H T U N G T R E N N U N G [Eq. (2)]).…”

“…The rearrangement of O-alkyl-substituted thiocarbonates leads to the well-known radical fragmentation (incorporated in the Barton-McCombie deoxygenation pathway) without the formation of rearrangement product (benzoate ester). [3] In contrast, radical fragmentation of C À N bonds through the same process is inefficient. For example, although reversible radical abstraction of the a-hydrogen readily occurs in amines, no scission of C À N bonds is observed under these conditions.…”

“…[a] Unless otherwise specified, all reactions were carried out at 11 mm of thiocarbamate, with the 1:2 molar ratio of radical initiator to Et 3 radical-stabilizing effect of the substituents. For example, thiocarbamates with para-OMe or -CN substituents do not show higher reaction yields.…”

Design of Leaving Groups in Radical CC Fragmentations: Through‐Bond 2c–3e Interactions in Self‐Terminating Radical Cascades

“… Selected examples of radical fragmentations in synthesis. Left: Scission of a weak CS is used to shift the equilibrium for an unfavorable rearrangement 10b–d. Center: Rare example of β‐scission of a CC bond, reported by Zard et al 10f.…”