Phosphine-Catalyzed Stereoselective Tandem Annulation Reaction for the Synthesis of Chromeno[4,3-b]pyrroles

Abstract

A phosphine-catalyzed tandem cyclization reaction has been developed to provide a series of chromeno [4,3-b]pyrrole derivatives, which contain three consecutive asymmetric centers. The reaction has a good yield, excellent stereoselectivity, and Z/E selectivity. The new method is simple, requires only mild conditions, and shows tolerance for various functional groups. Similarly, this reaction can be catalyzed by a chiral phosphine catalyst to achieve asymmetric synthesis. cascade cycloaddition strategy for facily synthesizing chromenopyrrole derivatives from aldimine esters and δ-acetoxy allenoates. In particular, a wide range of products have been afforded in generally good yields with excellent diastereoselectivities. In addition, by using a chiral phosphine catalyst, the cycloaddition reaction can also initially realize the asymmetric synthesis of chromeno [4,3-b]pyrrole. This protocol can be expected to find wide synthetic application because of its simple operation, mild reaction conditions, high efficiency, and high chemo-and enantioselectivity.

Organocatalyzed [2+2] Cycloaddition Reactions between Quinone Imine Ketals and Allenoates

“…1 H NMR (400 MHz, CDCl 3 ):  = 7.71 (d, J = 8.4 Hz, 2 H, ArH), 7.33-7.42 (m, 7 H, ArH), 7.23-7.24 (m, 1 H, ArH), 6.95-6.98 (m, 1 H, CH), 6.45 (d,J = 10.0 Hz,1 H,CH), 5.92 (s, 1 H, CH), 5.13 (s, 2 H, CH 2 ), 3.30-3.41 (m, 2 H, CH 2 ), 2.49 (s, 3 H, CH 3 ).…”

“…1 H NMR (400 MHz, CDCl 3 ):  = 8.03 (d, J = 8.0 Hz, 2 H, ArH), 7.57 (d, J = 7.6 Hz, 2 H, ArH), 7.15 (t, J = 8.8 Hz, 4 H, ArH), 7.09 (d,J = 11.2 Hz,2 H,CH), 6.37 (d, J = 11.2 Hz, 2 H, CH), 4.01-4.05 (m, 4 H, 2 × CH 2 ), 3.47 (s, 2 H, CH 2 ), 2.34 (s, 3 H, CH 3 ), 1.11 (t, J = 6.8 Hz, 3 H, CH 3 ).…”

“…1 H NMR (400 MHz, CDCl 3 ):  = 7.74 (d,J = 7.6 Hz,2 H,ArH),7 H,ArH), 6.91 (d, J = 9.6 Hz, 1 H, CH), 6.79 (d,J = 1.6 Hz,1 H,CH),1 H,CH), 5.84 (t, J = 2.0 Hz, 1 H, CH), 5.14 (s, 2 H, CH 2 ), 3.55-3.60 (m, 1 H, CH), 3.24-3.29 (m, 1 H, CH), 2.47 (s,3 H,CH 3 ).…”

“…1 H NMR (400 MHz, CDCl 3 ):  = 7.79 (d,J = 8.4 Hz,2 H,ArH),4 H,ArH),1 H,ArH),2 H,ArH),2 H,CH),2 H,CH), 6.06 (t, J = 2.0 Hz, 1 H, CH), 3.40 (d, J = 1.6 Hz, 2 H, CH 2 ), 2.50 (s, 3 H, CH 3 ).…”

Perfluoroalkyl-Promoted Synthesis of Perfluoroalkylated Pyrrolidine-Fused Coumarins with Methyl β-Perfluoroalkylpropionates

“…To improve the efficiency of [3 + 2] cycloaddition reactions with salicylaldehyde-derived azomethine ylides, enhanced Michael acceptors such as α,β-unsaturated ketophosphonates, ketoesters, allenoates, and benzylidene indan-1,3-diones are required as dienophiles (Scheme ). In some cases, additional activating reagents, including N-heterocyclic carbene, PPh 3 , or hydrogen-bonding molecules, ,, are employed for the promotion of such reactions. Furthermore, the α,β-unsaturated carbonyl with a good leaving group is necessary for the formation of the coumarin moiety by intramolecular esterification with the phenolic hydroxyl group. ,,, …”