Nitrous Oxide Promoted Pauson–Khand Cycloadditions

Abstract

A Pauson-Khand cycladdition of alkynes, alkenes, and carbon monoxide, promoted by cobalt carbonyl and nitrous oxide to furnish cyclopentenones is described. Preliminary mechanistic experiments suggest that nitrous oxide functions in a similar manner to the N-oxide promoters typically employed in Pauson-Khand reactions. Only dinitrogen and carbon dioxide are produced as a consequence of the activation mechanism, thus avoiding high molecular weight reagents and the build up of basic byproducts. The chemistry is done using equimolar amounts of alkyne, alkene, and dicobalt octacarbonyl, and is performed directly from the acetylenic component without having to presynthesize a cobalt-alkyne complex. Terminal acetylenes were suitable substrates, as was solid calcium carbide, and the corresponding adducts were isolated in good yields. Furthermore, two sequential [4+3] and [2+2+1] cycloadditions were performed, generating funtionalized cyclopentenones in only two steps from readily available starting materials.

Construction of all-carbon quaternary stereocenters by catalytic asymmetric conjugate addition to cyclic enones in natural product synthesis

“…Diyne 119 was subjected to a t-BuOK-catalyzed Conia-ene type cyclization 101 to give enyne 120 in 83% yield. A Pauson-Khand reaction 102 of enyne 120 mediated by Co 2 (CO) 8 in the presence of N 2 O 103 gave cyclized enone 121 in 59% yield with 93% ee. This was subjected to nickel-catalyzed methylation 104 to produce diketone 122 in 81% yield as a single diastereomer.…”

Acetylene and Ethylene: Universal C2 Molecular Units in Cycloaddition Reactions

“…Among them are tetracobalt dodecacarbonyl, 157 cobalt acetyl acetonate/sodium borohydride, 158 and mixtures of Co 2 (CO) 8 with nitrous oxide. 4c Of course, there are many other catalysts for Pauson–Khand processes, but here, we focus on examples that involve acetylene/ethylene. The process can be performed under thermal 1j 4c , 153 154 155 156 157 158 or microwave conditions.…”

Calcium‐Based Sustainable Chemical Technologies for Total Carbon Recycling

“…Another type of cycloaddition reaction with calcium carbide promoted by nitrous oxide is the Pauson–Khand reaction. The cobalt‐catalyzed intermolecular process leads to a cyclopentenone in a good yield …”

“…The cobalt-catalyzed intermolecularp rocess leads to ac yclopentenone in agood yield. [76] Isophorone is aw idely used building block in organic transformations.I ti sa lso used as as olvent with moderate polarity and high boiling temperature. Isophorone, deacetone alcohol, and mesityl oxide can be easily synthesized from inexpensive acetonet hrough calcium carbidec atalyzed trimerization (Scheme 8).…”