Asymmetric synthesis of dihydro-1,3-dioxepines by Rh(ii)/Sm(iii) relay catalytic three-component tandem [4 + 3]-cycloaddition

Catalytic asymmetric tandem carbonyl ylide formation/[4 + 3]-cycloaddition of β,γ-unsaturated α-ketoesters, aldehydes and α-diazoacetates was achieved by using a bimetallic rhodium(ii)/chiral N,N′-dioxide–Sm(iii) complex catalyst.

Recent advance in [3+2] cycloaddition of allene with 1,3-carbonyl ylide; Rh(II) catalyzed access to bridged polyoxocarbocyles

This prospective summarizes the stereochemical out comes of [3+2] cycloaddition of allene molecules with 1,3-dipolar carbonyl ylides derived from rhodium carbene mediated diazo decomposition for formation highly daistereoselective poly oxacarbocycle....

Tetrasubstituted Furans by Nucleophile-Induced Cleavage of Carbonyl Ylide–DMAD Cycloadducts

Compounds incorporating a 4-aza-8-oxabicyclo[3.2.1]oct-6-en-2-one moiety, which were prepared by a tandem carbenoid carbonyl ylide cyclization/[3+2]-cycloaddition reaction from ethyl 2-diazo-3-oxo-4-phthalimidobutanoates, undergo a nucleophile-induced two-bond ring cleavage when treated with protic heteronucleophiles. In this manner, tetrasubstituted furantricarboxylates, tethered with α-amino acids, esters, thioesters, and amides by a 2-carbonylphenyl moiety, are obtained.

Evolution of a Cycloaddition–Rearrangement Approach to the Squalestatins: A Quarter-Century Odyssey

The highs, lows, and diversions of a journey leading to two syntheses of 6,7-dideoxysqualestatin H5 is described. Both syntheses relied on highly diastereoselective n-alkylations of a tartrate acetonide enolate and subsequent oxidation–hydrolysis to provide an asymmetric entry to β-hydroxy-α-ketoester motifs. The latter were differentially elaborated to diazoketones which underwent stereo- and regioselective Rh(II)-catalysed cyclic carbonyl ylide formation–cycloaddition and then acid-catalysed transketalisation to generate the 2,8-dioxabicyclo[3.2.1]octane core of the squalestatins/zaragozic acids at the correct tricarboxylate oxidation level. The unsaturated side chain was either protected with a bromide substituent during the transketalisation or introduced afterwards by a stereoretentive Ni-catalyzed Csp3–Csp2 cross-electrophile coupling.1 Introduction 2 Racemic Model Studies to the Squalestatin/Zaragozic Acid Core3 Asymmetric Model Studies to a Keto α-Diazoester3.1 Dialkyl Squarate Desymmetrisation3.2 Tartrate Alkylation3.2.1 Further Studies on Seebach’s Alkylation Chemistry 4 Failure at the Penultimate Step to DDSQ 5 Second-Generation Approach to DDSQ: A Bromide Substituent Strategy 5.1 Stereoselective Routes to E-Alkenyl Halides via β-Oxido Phosphonium Ylides 5.2 Back to DDSQ Synthesis6 An Alternative Strategy to DDSQ: By Cross-Electrophile Coupling7 Alkene Ozonolysis in the Presence of Diazo Functionality: Accessing α-Ketoester Intermediates8 Summary

Alkylation of lithiated dimethyl tartrate acetonide with unactivated alkyl halides and application to an asymmetric synthesis of the 2,8-dioxabicyclo[3.2.1]octane core of squalestatins/zaragozic acids

(R,R)-Dimethyl tartrate acetonide 7 in THF/HMPA undergoes deprotonation with LDA and reaction at −78 °C during 12–72 h with a range of alkyl halides, including non-activated substrates, to give single diastereomers (at the acetonide) of monoalkylated tartrates 17, 24, 33a–f, 38a,b, 41 of R,R-configuration, i.e., a stereoretentive process (13–78% yields). Separable trans-dialkylated tartrates 34a–f can be co-produced in small amounts (9–14%) under these conditions, and likely arise from the achiral dienolate 36 of tartrate 7. Enolate oxidation and acetonide removal from γ-silyloxyalkyl iodide-derived alkylated tartrates 17 and 24 give ketones 21 and 26 and then Bamford–Stevens-derived diazoesters 23 and 27, respectively. Only triethylsilyl-protected diazoester 27 proved viable to deliver a diazoketone 28. The latter underwent stereoselective carbonyl ylide formation–cycloaddition with methyl glyoxylate and acid-catalysed rearrangement of the resulting cycloadduct 29, to give the 3,4,5-tricarboxylate-2,8-dioxabicyclo[3.2.1]octane core 31 of squalestatins/zaragozic acids. Furthermore, monoalkylated tartrates 33a,d,f, and 38a on reaction with NaOMe in MeOH at reflux favour (≈75:25) the cis-diester epimers epi- 33a,d,f and epi- 38a (54–67% isolated yields), possessing the R,S-configuration found in several monoalkylated tartaric acid motif-containing natural products.