Enantioselective access to tetrahydropyrano[2,3- c ]pyrazoles via an organocatalytic domino Michael-hydroalkoxylation reaction

Asymmetric Organocatalysis of Activated Alkynes and Enynes

“…Singh and co‐workers demonstrated the utility of trans ‐α‐alkynyl nitroolefins in enantioselective domino reaction via the Michael addition with ambident nucleophilic N ‐arylpyrazolinones 125 , followed by a hydroalkoxylation reaction to obtain enantioenriched tertahydropyranopyrazole motifs (Scheme 43). [70] This strategy provided enantioenriched pyrano‐annulated pyrazoles 139 with an exocyclic olefin with good yields and stereoselectivities under chiral bifunctional squaramide 23 m catalysis (65‐88% yield, >30 : 1 Z : E and 82–99% ee).…”

Metal‐Free Intramolecular Hydroalkoxylation of Alkyne: Recent Advances

“…In the same direction, Singh and co-workers also have applied such enantioselective Michael addition-hydroalkoxylation cascade for the synthesis of various tetrahydropyranopyrazole derivatives (Scheme 4). [16] They have used the same alkyne tethered nitro olefins as the Michael acceptor and have replaced 4-hydroxy coumarins with N-arylpyrazolinones. Thus, the reaction of N-arylpyrazolinones 4 with alkyne tethered nitro olefins 3 using 10 mol% of chiral bifunctional squaramide catalyst offered quick access to various tetrahydropyranopyrazoles 5 in good yield and excellent enantio-as well as diastereoselectivity.…”

An Unprecedented Organocascade Synthesis of Functionalized Bicyclic Nitrones from 2‐Aminomalonate Derived Nucleophiles and 1‐Nitro‐1,3‐Enynes via Allenes Formation and Subsequent Rearrangement

“…The use of conjugate nitro‐1,3‐enynes and related derivatives in this protocol has received much attention in recent years, including 2‐nitro‐1,3‐enynes ( 1 ), 1‐nitro‐1,3‐enynes ( 2 ) and alkyne‐tethered nitroalkenes ( 3 ) . Numerous chemical scaffolds that include nitrochromans (Xu), pyrano‐annulated derivatives (Chen,, Samanta, Singh), substituted pyrrole/thiophenes (Punniyamurthy),‐ tetrahydrofuranyl ethers (Krause, Alexakis), spirooxindole (Zhou), pyrano‐annulated pyrazoles (Enders), and spiropyrazolones (Schoenebeck, Enders) were prepared using these electron deficient enynes under either organocatalytic reaction conditions or sequential organocatalysis and metal catalysis (Figure ).…”