A novel four-component bicyclization
strategy has been established,
allowing a flexible and practical approach to 37 examples of multicyclic
pyrazolo[3,4-b]pyridines from low-cost and readily
accessible arylglyoxals, pyrazol-5-amines, aromatic amines, 4-hydroxy-6-methyl-2H-pyran-2-one, and cyclohexane-1,3-diones. The polysubstituted
cyclopenta[d]pyrazolo[3,4-b]pyridines
were stereoselectively synthesized through a microwave-assisted special
[3+2+1]/[3+2] bicyclization with good control of the spatial configuration
of exocyclic double bonds. The novel [3+2+1]/[2+2+1] bicyclization
resulted in 17 examples of unreported pyrazolo[3,4-b]pyrrolo[4,3,2-de]quinolones. Reasonable mechanisms
for forming two new types of multicyclic pyrazolo[3,4-b]pyridines are also proposed.
Readily available triethylammonium
1-(2-oxoindolin-3-ylidene)-2-aroylethanethiolates
are efficiently converted into a variety of fully substituted thiophene
derivatives by copper(I)-catalyzed denitrogenative reactions with
terminal alkynes and N-sulfonyl azides. This new
reaction simultaneously installs C–N, C–S, and C–C
bonds, allowing direct formation of highly functionalized thiophenes
with a wide diversity in substituents in a one-pot manner. A plausible
mechanism for the domino process is proposed.
A new three-component bicyclization for the efficient synthesis of a fused pyrano[2,3-b]pyridine library has been developed. The syntheses were achieved by reacting diverse C,O-containing nucleophiles, aldehydes, and 2-aminoprop-1-ene-1,1,3-tricarbonitrile under microwave irradiation, providing 50 examples of chemically and biomedically significant pyrano[2,3-b]pyridine analogues with the concomitant formation of two new rings and four σ bonds. This procedure features short reaction times, low-cost, and easily available starting materials, reliable scalability and mild reaction conditions, as well as operational simplicity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations –citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.