Regioselective Inter‐ and Intramolecular Formal [4+2] Cycloaddition of Cyclobutanones with Indoles and Total Synthesis of (±)‐Aspidospermidine

Abstract

Scheme 1. Selected natural products with a hydrocarbazole skeleton.Scheme 2. Formal [4+2] cycloaddition between indoles and 3-donorsubstituted cyclobutanones 6. PG= protecting group.

Selectivity Switch in a Rhodium(II) Carbene Triggered Cyclopentannulation: Divergent Access to Three Polycyclic Indolines

“…Protection of the indole nitrogen atom by other protecting groups, such as Bn and Ts, also resulted in excellent ratio selectivity. The Ts group proved to benefit the formation of the bridged product . For example, 5 h and 5 i were isolated in high yields as single isomers.…”

Synthesis and Reactivity of Donor-Acceptor Substituted Aminocyclopropanes and Aminocyclobutanes

“…Cyclobutanones, for example, can also be used as activated cyclobutanes [203,204]. The presence of the acceptor part on the four-membered ring allows the ring fragmentation by retro-aldol and subsequent annulation with various dipolarophiles [205]. The annulations that have been developed so far represent good alternative methods to the Diels-Alder cycloaddition for the construction of more saturated six-membered rings.…”

Total Synthesis of Aspidosperma and Strychnos Alkaloids through Indole Dearomatization

“…Recently,M atsuo and co-workers have reported an alternative cycloaddition procedure employing donor-acceptor cyclobutanes in combination with indoles (Scheme 16). [38] They found that for intermolecular[4+ +2]-cycloadditions, the temperature should be maintainedbetween À78 and À45 8C, whereas TiCl 4 should be used for optimal yields. To apply their method in the total synthesis of (AE)-aspidospermidine, the authors used an intramolecular approach with cyclobutanone 131.…”