Phosphine-catalyzed sequential (2+3)/(2+4) annulation of γ-vinyl allenoates: access to the synthesis of chromeno[4,3-b]pyrroles

Abstract

A phosphine-catalyzed cascade (2+3)/(2+4) cyclization reaction of γ-vinyl allenoates with aldimine ester has been developed to provide a series of chromeno[4,3-b]pyrrole derivatives, which contain three contiguous stereogenic centers. The method...

Phosphine-Catalyzed Internal Redox [4 + 2] Annulation between 1,4-Enynoates and Electron-Deficient Alkenes

“…According to the above results and literature, , a possible mechanism is illustrated in Scheme . An initial nucleophilic attack of phosphine on the alkyne of 1a forms a vinyl anion I that deprotonates the γ-carbon to form a resonance-stabilized zwitterion II .…”

Enantioselective, Decarboxylative (3+2)-Cycloaddition of Azomethine Ylides and Chromone-3-Carboxylic Acids

“…Due to the high significance of these two classes of compounds in drug discovery, the synthesis of compounds containing both of these two moieties is highly desirable [ 24 , 25 , 26 , 27 , 28 , 29 ]. To achieve this goal, decarboxylative 1,3-dipolar cycloaddition (1,3-DC) between carboxylic-acid-group-activated olefins and azomethine ylides was devised [ 23 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ] ( Scheme 2 ). Decarboxylative reactions constitute a very useful strategy in organic synthesis including stereoselective approaches [ 39 , 40 , 41 , 42 ].…”

DABCO-Catalyzed [4 + 2] Annulation of 5-Methylenehex-2-ynedioates with Electron-Deficient Alkenes

“…On the basis of these precedents, we were curious that 1,4-enynoates without φ-carbon, that is, 5-methylenehex-2-ynedioates 1a , might bring about a new reactivity. Of note is that compound 1a is reminiscent of γ-vinyl allenoates, which have been explored by Huang and co-worker to establish a set of phosphine-catalyzed tandem annulations. As our continuous interest in the Lewis base catalysis, , we now report a distinct amine-catalyzed [4 + 2] annulation of 5-methylenehex-2-ynedioates 1a with electron-deficient olefins for accessing highly functionalized spirocyclohexadienes in which the β- and ε-carbons of substrates are involved in bond formation (Scheme f).…”