Combining Silver Catalysis and Organocatalysis: A Sequential Michael Addition/Hydroalkoxylation One-Pot Approach to Annulated Coumarins

Abstract

A highly stereoselective one-pot procedure for the synthesis of five-membered annulated hydroxycoumarins has been developed. By merging primary amine catalysis with silver catalysis, a series of functionalized coumarin derivatives were obtained in good yields (up to 91%) and good to excellent enantioselectivities (up to 99% ee) via a Michael addition/hydroalkoxylation reaction. Depending on the substituents on the enynone, the synthesis of annulated six-membered rings is also feasible.

Silver-catalysed reactions of alkynes: recent advances

“…276 1,4-Enynes 380-2, in situ-generated by primary amine-catalysed stereo-controlled Michael addition of 379 to 380, underwent silver-catalysed intramolecular hydroalkoxylation reaction via a 5-exo-dig or 6-endo-dig mode to afford products 382 and 383, which was controlled by the substituent on the alkyne moiety. 276 1,4-Enynes 380-2, in situ-generated by primary amine-catalysed stereo-controlled Michael addition of 379 to 380, underwent silver-catalysed intramolecular hydroalkoxylation reaction via a 5-exo-dig or 6-endo-dig mode to afford products 382 and 383, which was controlled by the substituent on the alkyne moiety.…”

Applications of Thermal Activation, Ball‐milling and Aqueous Medium in Stereoselective Michael Addition of Nitromethane to Enynones Catalyzed by Chiral Squaramides

“…[7] These examples indicate promise for the development of new experimental methods where hydrogen-bonding catalysis enables attaining stereoselectivities observed under more standard conditions for asymmetric catalysis. [9] Such Michael acceptors with a triple bond in the conjugated system can react either in the 1,4- [10] or 1,6-mode (Scheme 1). [8] This reaction was exploited in an elegant synthesis of (+)-a-lycorane, where transformations of the remaining triple bond after conjugate addition were critical to the overall synthesis.…”

Catalyst‐Enabled Site‐Divergent Stereoselective Michael Reactions: Overriding Intrinsic Reactivity of Enynyl Carbonyl Acceptors

“…Hence,full synthetic potential of this class of vinylogous Michael technologies remains to be realized. [9][10][11] In contrast, 1,6-addition involves the generation of s-cis/transvinylogous enolates.T hus,regioselectivity and facial selectivity in the protonation of this intermediate should be controlled in concert with regio-and stereoselectivity of the initial carbon-carbon bond formation to obtain either enantioenriched allenes (ii)o rc onjugated dienes (iii)-(vi). Furthermore,s ynthetic utility of the unprecedented 1,6-addition system for enynyl carbonyl acceptors is clearly demonstrated by the concise derivatization of the configurationally defined, conjugated diene product to an ovel 2-amino-2-deoxysugar,2 -amino-2-deoxy-2-Me-d-altrofuranose derivative,b earing ac hiral tetrasubstituted carbon center.…”

“…We then thoroughly explored the scope with repsepct to the azlactones 3 in the 2i-catalyzed asymmetric 1,6-addition to 4.T he results listed in Table 2show that the incorporation of various alkyl and aryl groups onto the 4-position of 3 was tolerated and 1,6-g-Z,E-5 products were predominantly obtained with high stereoselectivities (entries [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. It should be noted that lowering the temperature to À40 8 8C was crucial for the additions of N-Ts-tryptophan-and phenylglycine-derived azlactones 3h and 3i,respectively,toproceed with rigorous enantiocontrol (entries 13 and 14).…”