Pauson-Khand reaction of activated olefins

Vinyl Sulfoxides as Stereochemical Controllers in Intermolecular Pauson–Khand Reactions: Applications to the Enantioselective Synthesis of Natural Cyclopentanoids

“…The same type of PK regioisomer has been previously reported from ethyl acrylate, acrylonitrile, and phenyl vinyl sulfone, [24] a fact suggesting that this 2,5-regioselectivity is a general trend for electron-deficient alkenes. [30] Interestingly, both the reactivity and the stereoselectivity proved to be highly dependent on the substitution at the sulfur center.…”

“…As these disappointing results could be due, at least partially, to the low thermal stability of the sulfinyl group, we turned to PK reactions promoted by amine N-oxides, which usually involve the use of very mild reaction conditions (usually 0 8C or room temperature). However, under the conditions reported by Cazes and co-workers (excess of NMO, CH 2 Cl 2 / THF, RT), [24,27] a sluggish reaction was observed, with the slow metal decomplexation of the alkyne dicobalt complex and recovery of the starting vinyl sulfoxide being the main result. To our delight a much faster reaction occurred when acetonitrile was used as the solvent.…”

“…In contrast to this general assumption, Cazes and co-workers reported in 1999 that certain sterically uncongested electron-poor alkenes, such as methyl acrylate and phenyl vinyl sulfone, gave good yields of PK adducts when the reactions were carried out in the presence of NMO as the promoter. [24] Our recent work on 1-sulfinyl-1,6-enynes [20] and 1-sulfonyl-1,6-enynes [25] in intramolecular PK reactions proved that, under appropriate experimental conditions, both a,b-unsaturated sulfoxides and a,b-unsaturated sulfones can be excellent substrates in this kind of process. [26] Taking into account all these precedents, we first explored the thermal reaction of vinyl sulfoxides 1 with the cobalt complex of 1-hexyne.…”

Pauson-Khand Reactions of Alkenyl Sulfones and Alkenyl Sulfoxides: Applications in Asymmetric Synthesis

“…Simultaneously with our work on intramolecular PKR of a,b-unsaturated sulfoxides and sulfones, Cazes et al reported 35 With respect to the topic of this Account, differently substituted 1-sulfonyl-3-hydroxy-1,6-enynes 4a-7a were readily prepared, as expected, by the piperidine-mediated condensation of the corresponding alkynyl aldehyde with phenylsulfonyl p-tolylsulfinyl methane and, eventually, further functionalization of the terminal alkyne (Scheme 10). Disappointingly, the first experiments, performed with alcohols 4a and 5a, showed that these substrates were hardly reactive under typical PKR conditions.…”

Five‐Membered Carbocycles

“…Cazes has shown that vinyl esters and sulfones participate in the intermolecur PKR under mild conditions: 0-20 °C and 6 equivalents of NMO. 101 The yields ranged from 0 to 59% for the esters and 49 to 71% for the sulfones. Acrylonitrile gave complex mixture of products under these same conditions.…”