Fe-Catalyzed Selective Cyclopropanation of Enynes under Photochemical or Thermal Conditions

Abstract

The nucleophilic Fe-complex Bu4N­[Fe­(CO)3(NO)] (TBA­[Fe]) catalyzes the cyclopropanation of enynes to substituted propargyl cyclopropanes using diazoesters as carbene surrogates. The catalyst can be activated either thermally in the presence of catalytic amounts of 4-nitroanisole or under photochemical conditions. Cyclopropanation occurs selectively at the enyne moiety; alternative olefinic moieties remain intact.

Transition‐Metal‐Free Cascade Enyne Rearrangement and Cyclopropanation of Allenylphosphine Oxides with N‐Tosylhydrazones Accessing Alkynylcyclopropane Derivatives

“…The strategies can be classified as follows: a) direct cyclopropanation of terminal alkynes with cyclopropane sources (including methylenecyclo‐propanes, [6a] cyclopropanol, [6b,c] cyclopropenes, [6d–g] and cyclopropyl iodides [6h–j] ) in the presence of a transition metal; b) reactions between alkenes and alkynylcarbenes, which are generated from dihalogenated alkynes, [7a,b] alkynyldiazoacetates compounds, [7c–f] propargyl alcohols, [7g] and alkynyl Fischer‐Carbene‐Complexes (FCCs); [7h–l] c) [2+1] cycloaddition reactions of conjugated enynes with propargyl pivalate, [8a] N ‐tosylhydrazones, [8b–e] diazo compounds, [8f–l] (iodomethyl)‐zinc species, [8m] or sulfur ylides; [8n] d) intramolecular cyclopropanation of functionalized alkynes [9]…”

Diastereoselective Synthesis of 1,3-Diyne-Tethered Trifluoromethylcyclopropanes through a Sulfur Ylide Mediated Cyclopropanation/DBU-Mediated Epimerization Sequence

“…Depending on the substitutions on the alkene moiety, both cyclopropanation and cyclopropenation products could be formed. For example, the reaction of 2-nonsubstituted 1,3-enynes with trifluorodiazoethane (CF 3 CHN 2 ) led to the formation of the desired cyclopropanation products, while exclusive cyclopropenation was observed for sterically more hindered 1-ethynylcyclohex-1-ene . Therefore, it is still highly desirable to develop an alternative synthesis for trifluoromethyl-substituted alkynylcyclopropanes from easily accessible and bench-stable starting materials in a highly chemo- and diastereoselective manner.…”

Iron: A Worthy Contender in Metal Carbene Chemistry

“…in great overall yields (Chart 7B). Alkyl ketones(129) were also obtained, albeit in variable yields. Yet, increased catalytic activity came at the cost of reduced…”

“…Unfortunately, similar conditions were not enough to allow olefin insertions. Only through a combination of in situ oxidative (with nitromethane) and photochemical (with blue light) decarbonylation, liberating two coordination sites in the iron center, were the authors able to combine EDA and enynes in good yields (see 161) 129. 4.3.…”