[3+2] regioselective annulation reaction of 2-arylidene-1,3-indandiones towards synthesis of spirocyclopentenes: understanding the mechanism of γ-attackvs.α-attack using DFT studies

Abstract

A [3+2] annulation protocol for the construction of functionalized spirocyclopentenes utilizing 1,3-indanedione derived benzylidene-1,3-indanedione and ethyl-2,3-butadienoate at room temperature was developed.

Phosphine‐Catalyzed [3+2] Cycloaddition of Aza‐Aurones and Allenoates: Enantioselective Synthesis of 2‐Spirocyclopentyl‐Indolin‐3‐Ones

“…Considering the obtained results and previous studies on phosphine‐catalyzed [3+2] cycloaddition between electron‐poor alkenes and allenoates, [16] including cyclizations of aurones [13a] and 2‐arylidene‐1,3‐indandiones, [13b] as well as applications of Kwon's phosphines in allenoate cycloadditions, [15,17] the mechanism that we proposed for the formation of 7 a is illustrated in Scheme 4. The nucleophilic attack of the phosphine on central sp carbon of allenoate 2 a generates the zwitterionic intermediate I , which possesses two resonance forms with the negative charge delocalized on the α‐ and γ‐carbon.…”

Chiral Isochalcogenourea‐Catalysed Enantioselective (4+2) Cycloadditions of Allenoates

“…In contrast, the use of PPh 3 gives the regioisomeric (3+2) cycloaddition products 5 [11] . In this case a first asymmetric proof‐of‐concept using chiral phosphines with low enantioselectivities was obtained, albeit leaving space for improvement [11b] . Accordingly, the establishment of alternative (chiral) catalyst motives for allenoate transformations could be a highly rewarding task.…”

“…[11] In this case a first asymmetric proof‐of‐concept using chiral phosphines with low enantioselectivities was obtained, albeit leaving space for improvement. [11b] Accordingly, the establishment of alternative (chiral) catalyst motives for allenoate transformations could be a highly rewarding task. With a suited complementary catalyst platform at hand, it should be possible to enter reaction pathways that are not possible with the existing catalysts, thus providing access to orthogonally functionalized product scaffolds, even in an asymmetric manner.…”

Chiral Isochalcogenourea‐Catalysed Enantioselective (4+2) Cycloadditions of Allenoates

“…[11] In this case a first asymmetric proof‐of‐concept using chiral phosphines with low enantioselectivities was obtained, albeit leaving space for improvement. [11b] Accordingly, the establishment of alternative (chiral) catalyst motives for allenoate transformations could be a highly rewarding task. With a suited complementary catalyst platform at hand, it should be possible to enter reaction pathways that are not possible with the existing catalysts, thus providing access to orthogonally functionalized product scaffolds, even in an asymmetric manner.…”