DABCO- and DBU-promoted one-pot reaction of N-sulfonyl ketimines with Morita-Baylis-Hillman carbonates: a sequential approach to (2-hydroxyaryl)nicotinate derivatives

Catalyst-Free α-Allylation of Dihydroisoquinolines with Morita-Baylis-Hillman Carbonates and Its Applications in the Construction of Benzo[a]quinolizidines

In this work, a mild and efficient catalyst-free α-allylation of 3,4-dihydroisoquinoline imines with Morita-Baylis-Hillman (MBH) carbonates was reported. The scopes of 3,4-dihydroisoquinolines and MBH carbonates as well as gram-scale synthesis were investigated, and densely functionalized adducts were obtained in moderate to good yields. The synthetic utility of these versatile synthons was further demonstrated by the facile synthesis of diverse benzo[a]quinolizidine skeletons.

Regioselective access to di- and trisubstituted pyridines via a metal-oxidant-solvent-free domino reaction involving 3-chloropropiophenones

A remarkable metal-oxidant-solvent- and base-free domino route for regioselective access to a wide range of 2,4-di- and 2,3,4/6-trisubstituted pyridines including carbo- and heterocyclic fused pyridines is reported. This [3C + 2C + 1N] cyclization reaction occurs between 3-chloropropiophenones (3C units), enolizable acyclic/cyclic ketones (2C sources) and NH₄OAc as a robust N source under neat conditions under an open atmosphere, producing new C=C and C=N-C bonds in highly chemo- and regioselective manners. Interestingly, this eco-friendly method has many positive features: excellent functional group tolerance, broad substrate scope, good to excellent regioselectivities, promising yields, no-unwanted products, neutral reaction conditions and appropriateness for large-scale synthesis. Mechanism studies reveal that the in situ generated β-amino ketone from 3-chloropropiophenone and an ammonium salt undergoes C=N bond formation with a ketone followed by an intramolecular cyclization process (C=C bond), which are the decisive steps for pyridine synthesis.

Cu(OAc)2/DABCO-mediated domino reaction of vinyl malononitriles with cyclic sulfamidate imines: access to 6-hydroxyaryl-2-aminonicotinonitriles

A novel Cu(II)-salt/DABCO-mediated one-pot access to a myriad of highly substituted biologically relevant 2-aminonicotinonitriles possessing a resourceful phenolic moiety with satisfactory yields is reported. This method involves cyclic sulfamidate imines as 1C1N sources and different kinds of acyclic/cyclic vinyl malononitriles as 4C sources for pyridine synthesis via a vinylogous Mannich-cycloaromatization sequence process, creating two new C-N bonds under mild conditions. Importantly, this de novo strategy is applicable to gram-scale syntheses, underlining the method's practicability and allowing for a wide range of substrates with excellent functional group tolerance.

Unmasking the reverse reactivity of cyclic N-sulfonyl ketimines: multifaceted applications in organic synthesis

The chemistry related to the exploration of cyclic N-sulfonyl ketimines and their derivatives has attracted significant attention in the last few decades because of their intriguing structures and properties. They serve broadly as reactive synthons in various reactions to create a diverse set of synthetically and biologically attractive molecules. Furthermore, these moieties, which possess multiple heteroatoms (N, O and S), display or can enhance many biological activities. In the case of synthetic reactions, chemists mainly focus on the chemical manipulation of the highly reactive prochiral CN bond of N-sulfonyl ketimines. Besides their traditional role as electrophiles, N-sulfonyl ketimines possess α-Csp³-H protons, and thus behave as potential carbonucleophiles, where they can undergo several C-X (X = C, N and O) bond-forming reactions with different types of electrophiles under various conditions to form a wide range of fascinating asymmetric and non-asymmetric versions of fused heterocycles, carbocycles, spiro-fused skeletons, pyridines, pyrroles, etc. Herein, we highlight the recent examples from our research work and others covering the scope of cyclic N-sulfonyl ketimines as useful carbonucleophiles. In addition, the detailed mechanistic studies of the above-mentioned reactions are also presented.

NH4OAc-Promoted Domino Route to Hydroxyarylated Unsymmetrical Pyridines under Neat Conditions

A new metal-, oxidant-, and solvent-free ecofriendly domino method has been established for modular synthesis of a diverse range of medicinally promising hydroxyarylated unsymmetrical pyridines in good to high chemical yields with an excellent regioselectivity. This domino process involves a range of N-sulfonyl ketimines as C,N-binucleophiles, enolizable ketones, and aromatic/heteroaromatic aldehydes using ammonium acetate as an ideal promoter under neat conditions, which creates two new C-C bonds and one C-N bond. Notably, the neutral reaction conditions are mild enough to tolerate a range of functionalities and cover a variety of substrates, thus bestowing a powerful avenue to access tri- and tetrasubstituted pyridines including carbo- and heterocyclic fused ones. Interestingly, a practical, scalable, and high-yielding synthesis of pyridylphenol derivatives was successfully accomplished by our unique method.

1,6-Addition of vinyl p-quinone methides with cyclic sulfamidate imines: access to 4-hydroxyaryl-2,6-diarylpyridines

A base-promoted 1,6-addition–cyclization reaction of vinyl para-quinone methides with cyclic sulfamidate imines in an open atmosphere is reported. This method delivers good to high yields of 2,4,6-trisubstituted pyridines with a valuable phenolic moiety at the C4-position.

Chemoselective cyclization of N-sulfonyl ketimines with ethenesulfonyl fluorides: access to trans-cyclopropanes and fused-dihydropyrroles

A stereo- and chemoselective ring closing reaction of N-sulfonyl ketimines with ethene sulfonyl fluorides promoted by DBU is reported. This selective C–C vs. C–N bond cyclization process delivers to trans-cyclopropanes (dr up to ≤99 : 1) and fused-dihydropyrroles.