p-Nitrophenyl carbonate promoted ring-opening reactions of DBU and DBN affording lactam carbamates

Abstract

SummaryThe amidine bases DBU (1,8-diazabicyclo[5.4.0]undec-7-ene) and DBN (1,5-diazabicyclo[4.3.0]non-5-ene) display nucleophilic behaviour towards highly electrophilic p-nitrophenyl carbonate derivatives with ring opening of the bicyclic ring to form corresponding substituted ε-caprolactam and γ-lactam derived carbamates. This simple method presents a unified strategy to synthesize structurally diverse ε-caprolactam and γ-lactam compounds with a large substrate scope.

Chromatography‐Free Multicomponent Synthesis of Thioureas Enabled by Aqueous Solution of Elemental Sulfur

“…In fact, the activation energy of ammonium ion formation is very low, [67] and thus we suppose a dynamic equilibrium between the quaternization of the terminal and the middle nitrogens. The nucleophilicity of DBU and related amidines DBN, TBD and MTBD has been used in their reactions with aldehydes, [68] carbonates, [69] imidazolides, [70] methyl-pyrazoles [71] and benzoxazinones [72] as electrophiles leading to caprolactams or substituted tetrahydropyrimidinones. Notably, cyclic amidines undergo ring-opening in the presence of water yielding aminopropyl lactams and pyrimidinones that readily react with halobenzenes [73][74][75] and esters.…”

DBU: A Reaction Product Component

“…A number of processes gathered in this review could most probably be extended to reactions with 1,5‐diazabicyclo[4.3.0]non‐5‐ene (DBN). Indeed, DBN display properties similar to those of DBU, and reports describing similar results are already available …”

“…p-Nitrophenyl carbonates, which are highly electrophilic species, underwent ring opening of DBU giving ε-caprolactam derived carbamates (Scheme 28a). [55] The reaction occurs via nucleophilic addition of DBU to the carbonate affording 28A which suffers attack of water leading to 28B (Scheme 28b). Subsequent ring opening gives the product.…”

“…Indeed, DBN display properties similar to those of DBU, [8] and reports describing similar results are already available. [13,18,20,30,34,40,43,44,46,49,50,51,55,62,70,73,[75][76][77][78]…”

N-Heterocyclic Olefin Catalysis for the Ring Opening of Cyclic Amidine Compounds: A Pathway to the Synthesis of ε-Caprolactam- and γ-Lactam-Derived Amines

“…The role of DBN or DBU as a sterically hindered, weakly nucleophilic amidine-type strong base and catalyst is well-known, especially in dehydrohalogenation reactions, but some reports in the literature revealed their ability to act as nucleophiles . Their capacity to act as nucleophile led to some unexpected results, as revealed by the ring opening of the bicyclic amidine reported for the first time by Lammers in 1994 and followed by a few others involving as ultimate product, ε-caprolactam derivatives. − The nucleophilic character of DBU and DBN was observed in the reaction with carbonyl electrophilic species, namely, methyl esters, p -nitrophenyl carbonate, imidazolides, and benzoxazinones, on the hydrolysis of amide carbonyls or even in palladium-catalyzed carbonylation reactions, in all cases leading toward lactams resulting from the ring opening of the cyclic amidine. , …”