Biosynthesis of oxygen and nitrogen-containing heterocycles in polyketides

• Franziska Hemmerling and
• Frank Hahn

Beilstein J. Org. Chem. 2016, 12, 1512–1550, doi:10.3762/bjoc.12.148

• salinosporamide A (199) (Scheme 27) [160][161]. Based on gene cluster analysis, it was proposed that both heterocycles of this PKS–NRPS hybrid product, an oxetan-2-one and a pyrrolidin-2-one, are formed by a bicyclisation mechanism. Aldol addition of the amino acid α-position on the carbonyl gives the pyrrolidin

Synthesis of the furo[2,3-b]chromene ring system of hyperaspindols A and B

• Danielle L. Paterson and
• David Barker

Beilstein J. Org. Chem. 2015, 11, 265–270, doi:10.3762/bjoc.11.29

• been achieved in twelve steps. By comparison of the NMR spectra of the synthesized compounds with those of the natural products, a relative stereochemistry is suggested, especially that of the ketal carbon. Keywords: acylphloroglucinols; bicyclisation; furo[2,3-b]chromene; fused ketal; Introduction

Palladium-catalysed cyclisation of alkenols: Synthesis of oxaheterocycles as core intermediates of natural compounds

• Miroslav Palík,
• Jozef Kožíšek,
• Peter Koóš and
• Tibor Gracza

Beilstein J. Org. Chem. 2014, 10, 2077–2086, doi:10.3762/bjoc.10.216

• synthetic construction of substituted tetrahydrofurans. Recently, we have described a novel type of PdCl2/CuCl2-catalysed bicyclisation reaction of α-O-benzyl-protected sugar-derived alkenitols A, that provided 2,5-dioxabicyclo[2.2.1]heptanes B with high 1,4-threo-selectivity (Scheme 1) [22][23]. In this

• substituents to cover certain possibilities for Pd-catalysed cyclisation screening. At first, easily accessible C5-alkenitols (Figure 2) were chosen as simplest suitable substrates for screening the optimal reaction conditions of the previously described bicyclisation reaction. Thus, the known triols erythro-9

• bicyclisation of α-O-benzyl-protected polyols bearing a terminal alkene moiety [22]. Thus, the reactions incorporating the PdII–Pd0 catalytic cycle (Scheme 6) were carried out using PdCl2 (0.1 equiv) as a catalyst, CuCl2 (3 equiv) as a reoxidant, NaOAc (3 equiv) as a buffer in AcOH at room temperature (Table 1

Two-directional synthesis as a tool for diversity-oriented synthesis: Synthesis of alkaloid scaffolds

• Kieron M. G. O’Connell,
• Monica Díaz-Gavilán,
• Warren R. J. D. Galloway and
• David R. Spring

Beilstein J. Org. Chem. 2012, 8, 850–860, doi:10.3762/bjoc.8.95

• a nucleophilic amino group with suitable electrophilic functionality, provided by Michael acceptor α,β-unsaturated ester groups. Two-directional synthesis was used to append these electrophilic groups at two positions around the linear substrates, allowing bicyclisation processes to be instigated

• chloroacetamide with thiourea gave the free amine [21], which was then protected with Boc anhydride. Finally, cross metathesis with ethyl acrylate furnished the desired compound 4 in 24% overall yield. Cyclisation reactions The first attempts at the tandem Boc-deprotection/bicyclisation of these substrates were

• performed by using AlCl3 as the Lewis acid (Scheme 2); compounds 1–4 were treated with 1.1 equiv of AlCl3 in dichloromethane at room temperature. These conditions proved effective at promoting bicyclisation for compounds 1, 2 and 4, for which the desired bicyclic products were obtained in 67–85% yield, as a