Total Synthesis of (−)-Ambiguine P

Abstract

Described is a concise total synthesis of (−)-ambiguine P, a cycloheptane-containing member of the hapalindole alkaloids. The challenging pentacyclic framework of the natural product was assembled rapidly via a [4 + 3] cycloaddition reaction-inspired strategy, and the tertiary hydroxy group was introduced by an NBS-mediated bromination–nucleophilic substitution sequence.

Recent Advances in Transition-Metal-Free (4+3)-Annulations

“…A recent report by Rawal employs an atypical two-step strategy to enable a '(4+3)-annulation' towards the synthesis of the core scaffold of (-)-ambiguine P (Scheme 5.1.14). 97 Although model studies using simpler dienes worked well with TMSOTf in CH 2 Cl 2 , the desired diene only formed the first C-C bond. Further reaction in the presence of NaAuCl 4 •2H 2 O in i-PrOH afforded the desired cycloadduct.…”

Facile synthesis of the spiro-pyridoindolone scaffoldviaa gold-catalysed intramolecular alkynol cyclisation/hydroindolylation

“…2 In this context, domino processes that combine the gold-catalysed π-activation of alkynes and subsequent indole functionalization, have been established as a promising approach for the synthesis of complex polycyclic indole derivatives, and also for the synthesis of indole-based natural products. 3 The synthesis of the tetracyclic indole skeleton via the intramolecular cyclisation of indole-tethered alkynols/ynamides and the trapping of the resultant electrophilic intermediate with the oxygen-centred nucleophile in the presence of a gold complex has been pioneered by the groups of Bandini and Gong–Yang respectively. 4,5 Likewise, the addition of carbon centred nucleophiles to the C2 of indole was explored by the Ohno, Huang, and Liu groups.…”

Total Syntheses of Aspidospermidine, N-Methylaspidospermidine, N-Acetylaspidospermidine, and Aspidospermine via a Tandem Cyclization of Tryptamine-Ynamide

“…To verify the feasibility of this strategy for installation of the ethyl group, Suzuki–Miyaura coupling was first attempted but proved to be ineffective in providing the product, instead resulting in the formation of the deiodination product. Next, different conditions for the Stille cross-coupling reaction of compound 8 were screened . The reactions using palladium catalysts such as Pd­(PPh 3 ) 2 Cl 2 , Pd­(PPh 3 ) 4 , and Pd­(dppf) 2 Cl 2 in N , N -dimethylformamide (DMF) at 120 °C were also unsuccessful in affording the desired compound 7 , leading only to the isolation of deiodination byproduct 18 (Table , entries 1–3).…”