Reactions of α,β‐Enones with Diazo Compounds, Part 3

Abstract

Carbonyl ylides arising from ethyl acetodiazoacetate/dimethyl diazomalonate and α,β‐enones with mainly s‐cis conformations underwent disrotatory cyclization to produce dihydrofuran derivatives. This process proved to be sensitive to steric effects. The corresponding ylides arising from rather s‐trans α,β‐enals yielded dioxole derivatives. The mechanisms of the reactions are discussed.

Metal-Catalyzed Cyclization Reactions of Carbonyl Ylides: Synthesis and DFT Study of Mechanisms

“…This was in complete contrast to our previous findings, because all R,β-unsaturated ketones we experimented with ended up with dihydrofuran type products. [5][6][7][8] Product 7 actually contained two stereoisomers, 7a and 7b, which were inseparable in our hands. On the other hand, the crude mixture was investigated by both GC-MS and 1 H NMR and no evidence for a possible formation of a furan (6) product was found.…”

“…Alternative Cyclization Reaction Starting from the Carbonyl Ylides: Dihydrofuran Formation. Various R,βunsaturated carbonyl compounds with the same [6][7][8] or different metal catalysts 4 gave the dihydrofuran derivatives as products. To complete the overall picture of the cyclization reactions of carbonyl ylides in the presence of copper catalysts, modeling of an alternative path leading to the dihydrofuran product was necessary for our purposes.…”

Reactions of α,β‐Enones with Diazo Compounds. Part 4

“…The (Z)-enones (Z)-2 and (Z)-7, and enone 6 (with an additional Me substituent at C(2) C(b)) did not give any dihydrofuran derivatives, as expected from the prerequisite of both termini being closest to each other (C(1) and C(5) in the transition state of Scheme 1) for an electrocyclic 1,5-ring closure reaction [1]; instead …”

“…± Dioxole and dihydrofuran derivatives are among the mostsignificant heterocycles in natural products, and consequently a wide range of methods for their syntheses has been developed [2 ± 8]. We previously reported the reactions of several a,b-enones and -enals with ethyl acetodiazoacetate and dimethyl diazomalonate (DMDM) in the presence of (acetylacetonato)copper(II) ([Cu(acac) 2 ]) [1] [9] [10]. In these reports, we noted that under mild conditions, dihydrofuran derivatives such as 3 ± 5 should be formed predominantly, by a 1,5-electrocyclic ringclosing reaction of the related carbonyl ylides derived from properly chosen (E)enones existing mainly as s-cis conformers.…”

Synthesis of Highly Functionalized γ‐Lactones via 1,5‐Electrocyclic Ring Closure

“…These predictions should also furnish a tool to rationalize the product distribution of the catalytic reaction with DMDM. In all of our previously used enones that yielded dihydrofuran derivatives [2] [10] in a pericyclic reaction, the C=O ··· C(b) distances were less than ca. 2.9 Å.…”