Fluoride-Assisted Activation of Calcium Carbide: A Simple Method for the Ethynylation of Aldehydes and Ketones

Abstract

The fluoride-assisted ethynylation of ketones and aldehydes is described using commercially available calcium carbide with typically 5 mol % of TBAF·3H2O as the catalyst in DMSO. Activation of calcium carbide by fluoride is thought to generate an acetylide "ate"-complex that readily adds to carbonyl groups. Aliphatic aldehydes and ketones generally provide high yields, whereas aromatic carbonyls afford propargylic alcohols with moderate to good yields. The use of calcium carbide as a safe acetylide ion source along with economic amounts of TBAF·3H2O make this procedure a cheap and operationally simple method for the preparation of propargylic alcohols.

Visible light mediated metal-free thiol–yne click reaction

“…In the first step, alkyne 1a was prepared according to the published procedure. 17 Alkyne 1a was converted to vinyl sulfide 3a using the developed photochemical protocol. Dehydration of 3a under mild conditions furnished diene 8a in 94% isolated yield.…”

Calcium Carbide: A Unique Reagent for Organic Synthesis and Nanotechnology

“…It should be mentioned that only the α‐branched compounds participated in the reaction; no interaction at all was observed for benzaldehyde (Scheme A, C). A seminal recent discovery of Schreiner and co‐workers revealed a crucial role of fluoride ions in the reaction between acetylene and ketones (Scheme B) . It is possible that fluoride from TBAF ⋅ 3 H 2 O activates ethynylcalcium hydroxide, which is formed from the reaction of water with solid calcium carbide.…”

“…As eminal recent discovery of Schreiner and co-workersr evealed ac rucial role of fluoridei ons in the reactionb etween acetylene and ketones (Scheme 8B). [40] It is possible that fluoride from TBAF·3H 2 Oa ctivates ethynylcalcium hydroxide, which is formed from the reactiono fw ater with solid calcium carbide. The corresponding "ate" complex attacks the carbonyl component to give the propargylic alcohols.…”

Using Calcium Carbide as an Acetylene Source for Cascade Synthesis of Pyrrolo[2,3‐b]quinoxalines via Copper‐Free Sonogashira Coupling Reaction

“…In 2015, Seidel and Schreiner reported a simple method for the ethynylation of aldehydes and ketones by fluoride‐assisted activation of calcium carbide. In this method, the reaction of water with solid calcium carbide gives ethynylcalcium hydroxide, which is activated by fluoride from TBAF · 3 H 2 O to form the corresponding ate‐complex that attacks the carbonyl compounds . In this article, the restrictions of procedure due to the aldol condensation of carbonyl compounds in the basic medium or steric and torsional strains have been explained.…”

“…In this article, the restrictions of procedure due to the aldol condensation of carbonyl compounds in the basic medium or steric and torsional strains have been explained. A p K a value of 26.4 for the carbonyl component was considered as a lower limit to avoid an aldol condensation …”