Intramolecular Cycloaddition of Isomunchnone Dipoles to Heteroaromatic .pi.-Systems

Synthesis and Functionalization of Indoles through Rhodium-Catalyzed Reactions

“…Padwa and coworkers reported the first example of rhodium(II) catalyzed intramolecular cycloaddition of isomunchnones to indole dipolarophiles (Scheme 38) [75]. The cyclic diazo imide (112) gave the ployheterocyclic indole derivative (113) as shown in scheme 39.…”

Rhodium(II)‐Catalyzed 1,3‐Dipolar Cycloaddition Reactions

“…Examples include the cycloaddition with aldehydes [43] and their generation from diazo imides [44]. Specific examples include bimolecular cycloaddition [48], cycloaddition with heteroatomic p-systems [49], and the formation of polyheterocyclic ring systems [50]. Specific examples include bimolecular cycloaddition [48], cycloaddition with heteroatomic p-systems [49], and the formation of polyheterocyclic ring systems [50].…”

“…Diastereoselectivity is achieved by controlling the orientation of the dipolarophile as it approaches the dipole, resulting in either an exoor endo-cycloaddition product [47]. In the case of intramolecular cycloadditions, in the absence of electronic effects, the exo/endo ratio is mainly controlled by steric factors [49,91,92]. In the case of intermolecular cycloaddition reactions with electron-deficient dipolarophiles, low selectivities are observed and the exo/endo ratios are largely case-dependent [47,87].…”

Tandem Methodology for Heterocyclic Synthesis

“…When the side chain is devoid of a carbonyl group, the calculated reaction barrier is much larger, thereby permitting competing cycloaddition of α-diazoimide 23. Cycloaddition of the initially formed dipole across the pendant indole π-system [49] would be expected to result in the simultaneous generation of the CD-rings of the aspidosperma skeleton [50]. The stereospecific nature of the internal cycloaddition reaction should also lead to the correct relative stereochemistry of the four chiral centers about the C-ring.…”