Two Contrasting Asymmetric Approaches to Muscarine Based on 5‐endo‐trig Cyclisations

Abstract

Keywords: Cyclisation / Muscarine / Oxygen heterocycles / Enantioselectivity / Natural products 5-endo-trig cyclisation of the (Z)-hydroxyalkenoate 17 using iodine as the electrophile gave a good yield of the β-hydroxytetrahydrofuran 18, probably via the corresponding iodohydrin. A variety of one-carbon degradation methods were then used to generate precursors to (−)-muscarine (25d). An alternative strategy featured control of a 5-endo-trig iodocyclisation by an allylic hydroxyl group, which can be used for the highly stereocontrolled synthesis of hydroxy-iodote-

Synthesis of α‐Hydroxyallenes by Copper‐Catalyzed SN2′ Substitution of Propargylic Dioxolanones

“…After further 5 min, compound 1a (4 mmol, 512 mg) was added in one portion and the resulting slurry was stirred until all starting material was consumed. 5-Phenylpent-4-yne-2,3-diol (2b): [29] Compound 1b (1.42 g, 10 mmol), NaIO 4 (3.2 g, 15 mmol), RuCl 3 (0.5 mL, 0.1  in H 2 O), H 2 SO 4 (2 mL, 1 ) and NaOAc/MeCN/H 2 O (30 mL:30 mL/ 7.5 mL) were treated the same procedure as 2a. -1-ynyl)cyclohexane-1,2-diol (2c): [30] Compound 1c (1.20 g, 10 mmol) and K 3 Fe(CN) 6 -1-ynyl)-4-methyl-1,3-dioxolan-2 4 ] (0.1 mmol, 10 mol-%), (BuO) 3 P (0.2 mmol, 20 mol-%) and CH 2 Cl 2 (2 mL), the mixture was stirred at room temp.…”

Expedient Syntheses of β‐Iodofurans by 5‐endo‐dig Cyclisations

“…Yields quoted are an average of those obtained using the specified conditions; variations were typically around 5-8 %. Iodo-5-methyl-2-phenylfuran (15d): By the general procedure, iodocyclisation of the alkynediol 14d [20] …”

Synthesis of Secondary Metabolites from Higher Fungi

“…Two years after the publication of their newly developed method to synthesise 89 (see Scheme 12), Knight and coworkers applied a similar methodology to create the (-)-enantiomer of 89 (Scheme 14). 114 The known epoxide 106 was used as starting material. Alkylation with lithiopropyne generated the homopropargylic alcohol 107 which was transformed into the tetrahydrofuran derivative 108 via Lindlar reduction and iodine-mediated cyclisation.…”

“…Methyl bovinate (114) is an example of a structurally more complicated pulvinone derivative, featuring an additional lactone ring (Figure 8). It was first isolated from Suillus bovinus by Steglich and co-workers in 2008.…”