Transition Metal Free Cycloamination of Prenyl Carbamates and Ureas Promoted by Aryldiazonium Salts

Abstract

Upon treatment with aryldiazonium salts, prenyl carbamates and ureas undergo redox-neutral azocycloamination. In general, N-aryl O-prenyl carbamates cyclize in a photocatalytic reaction with visible light and an organic dye. With electron-deficient diazonium salts, electronic matching with an electron-rich N-aryl substituent results in a reaction proceeding in the ground state, without either light or photocatalyst. Cyclic voltammetry suggests that this radical reaction is initiated by hydrogen-atom abstraction mediated by an aryl radical, followed by a radical addition cascade and proton-coupled hole propagation. The reaction proceeds at room temperature in short reaction times, and a range of functional groups is tolerated.

A Facile Direct Route to N‐(Un)substituted Lactams by Cycloamination of Oxocarboxylic Acids without External Hydrogen

“…To explore this opportunity,s everalc ontrole xperiments were conducted. [5][6][7][8][9][10][11]. [16] Second, H 2 NCHO can be hydrolyzed in water with conversions up to around7 0% after 1.5 ha t1 60 8Ca nd were then constant upon prolonged reactiont o4h.…”

“…[16] Second, H 2 NCHO can be hydrolyzed in water with conversions up to around7 0% after 1.5 ha t1 60 8Ca nd were then constant upon prolonged reactiont o4h. Ta ble 1s hows that systemsd epending on metal catalysts require much longer reaction times (up to 72 h) to achieve moderate yields of either substituted or unsubstitutedl actams (entries [8][9][10][11], despite relativelyl ow reaction temperatures (25-130 8C). As expected, the addition of water (30 equiv) into the reactions ystemsw ith and withoutH COOH ( Table 1, entries 3a nd 4) significantly acceleratest he cycloamination reaction, providing comparable MPD yields of 92 and 94 %.…”

“…An attractive approachtosecondary lactams is catalytic cyclizationo fp rimary amides with intramolecular alkenes in the presence of metal catalysts via aza-Heck or aza-Wacker mechanisms, in spite of the need to use, respectively,h ighly electrophilic or nucleophilic nitrogen species. [9] All of these approaches require specific catalysts and/ora dditives, as wella s organic solvents, to afford satisfactory yields.T herefore, it would be desirable to develop ac atalyst-and solvent-free methodf or the construction of valuablel actam skeletons from sustainable and low-costsubstrates. [9] All of these approaches require specific catalysts and/ora dditives, as wella s organic solvents, to afford satisfactory yields.T herefore, it would be desirable to develop ac atalyst-and solvent-free methodf or the construction of valuablel actam skeletons from sustainable and low-costsubstrates.…”

“…[4] Lactams can also be obtained in other ways, such as by combiningh omoenolates with acid-activated imines, [5] intramolecular hydrocarbamoylation of allylic formamides, [6] Michael addition-proton transfer-enol lactonization of acyl chlorides with dicarbonyls, [7] intramolecular alkenylation of acyclicb romoalkenes, [8] and cycloamination of prenyl carbamates and ureas. [9] All of these approaches require specific catalysts and/ora dditives, as wella s organic solvents, to afford satisfactory yields.T herefore, it would be desirable to develop ac atalyst-and solvent-free methodf or the construction of valuablel actam skeletons from sustainable and low-costsubstrates.…”

Transition‐Metal‐Free Deconstructive Lactamization of Piperidines

“…[5] Fortunately,aconsiderable number of remarkable transition-metal-free synthetic protocols are reported daily. [6][7][8][9][10] In recent years,o ur research group has developed efficient, accessible,e conomic,a nd environmentally friendly protocols for the functionalization of simple N-heterocycle substrates to give relevant bioactive precursors. [11] Thesuccess of this direct functionalization of pre-existing N-heterocycles lies in the highly selective CÀHo xidation at the a position mediated by cheap and environmentally friendly reagents such as NaClO 2 ,N aOCl, and 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO), in which, under modulated conditions,t he C À Hoxidation at the b position can be achieved, even under catalytic conditions.…”