Synthesis and chemistry of a stabilized dehydrosecodine model system

Abstract

of browniine, 107 mg (1.05 mmol) of (S)-(+)-2-methylbutyric acid ([a]22!) +19.3°( CH2C12)), 217 mg (1.05 mmol) of DCC, and 32.1 mg (0.26 mmol) of DAP in 10 mL of dichloromethane was heated at reflux for 20 h. The usual workup procedure furnished 74 mg of crude product which was placed upon a column containing 15 g of alumina (activity III). The column was eluted with ethyl acetate to yield 62.2 mg (61%) of 14-(2-methylbutyryl)browniine (10), mp 110.5-111.5 °C. Recrystallization from hexane/acetone twice afforded 10 with a melting point of 113-118 °C and [a]17D +39.9°(c, 0.72, MeOH), in excellent agreement with the corresponding measurements for a sample of glaucedine isolated from the plant.

The intramolecular Diels–Alder reaction: recent advances and synthetic applications

“…Nevertheless, increasing circumstantial evidence is provided by a number of laboratory cyclizations under mild conditions to give the natural ring systems. An example of the caution required is provided by a recent synthesis of a stabilized dehydrosecodine which failed to undergo the anticipated intramolecular cycloaddition(s) to the alkaloid skeleton(s) (267) even though other evidence suggests some Aspidosperrna and Iboga skeletons may be formed in this way (68 -70, 1 13,269).…”

Biogenetically inspired synthesis and skeletal diversification of indole alkaloids

“…Taking into account for the experimental results on the conversions of deuterium labeled 14a (see Supplementary Schemes S1-S2), 28 could presumably be formed through a hydride shift generating a zwitterionic intermediate composed of a pyridinium cation and an enolate anion, which would undergo subsequent 7-endo cyclization. 28 In contrast to the identical conversion of 13a into 14a under gentle heating at 60 °C, yielding the iboga-skeleton (23) as the major product (Fig. 3), 23 was not obtained at all at 120 °C.…”

Mechanistic Dichotomy with Alkynes in the Formal Hydrohydrazination/Fischer Indolization Tandem Reaction Catalyzed by a Ph3PAuNTf2/pTSA Binary System

“…2‐(2‐Ethyl‐1 H ‐3‐indolyl)‐1‐ethanol (3t′): 34 Yield 13 mg (20 %); viscous oil; R f = 0.48 (hexane/EtOAc, 60:40). 1 H NMR (300 MHz, CDCl 3 ): δ = 7.86 (br.…”