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Updated: Jun 13, 2025
Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes
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1,2-Dihydropyrimidine synthesis via titanium-mediated multicomponent coupling of alkynes, nitriles, and aldehydes
Rachel J Dunscomb1, Connor W Frye1, Xavier Murray1
1Department of Chemistry, University of Minnesota-Twin Cities, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, USA. itonks@umn.edu.
Abstract:
While dihydropyrimidine cores are found in a number of bioactive molecules, 1,2-dihydropyrimidine regioisomers remain relatively underexplored due to a scarcity of simple synthetic routes to access them. Here, a modular, multicomponent synthesis to 1,2-dihydropyrimidines from alkynes, nitriles, aldehydes, and Ti imido complexes is reported, proceeding through a key diazatitanacycle intermediate that was previously exploited for pyrazole and α-diimine synthesis. The 1,2-dihydropyrimidines are formed through [2+2]-cycloaddition of an aldehyde with the diazatitanacycle synthetic intermediate, followed by cycloreversion to a 1,5-diazatriene that undergoes facile electrocyclization to the 1,2-dihydropyrimidine.
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01:22Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
02:34Preparation of Alkynes: Dehydrohalogenation
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
02:27Preparation of Alkynes: Alkylation Reaction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
02:40Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.