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For terminal alkynes it is sometimes important to mask the acidic hydrogen atom. This normally proceeds from deprotonation (via a strong base like methylmagnesium bromide or butyllithium in tetrahydrofuran/ dimethylsulfoxide ) and subsequently reaction with chlorotrimethylsilane to a terminally TMS-protected alkyne. [ 95 ]
Hydroaluminations of terminal alkynes typically produce terminal alkenylalanes as a result. Selectivity in hydroaluminations of internal alkynes is typically low, unless an electronic bias exists in the substrate (such as a phenyl ring in conjugation with the alkyne).
Terminal alkynes have the formula RC≡CH, where at least one end of the alkyne is a hydrogen atom. An example is methylacetylene (propyne using IUPAC nomenclature). They are often prepared by alkylation of monosodium acetylide. [4] Terminal alkynes, like acetylene itself, are mildly acidic, with pK a values of around 25.
An alternative is the direct coupling of an acyl chloride with a terminal alkyne, using a copper-based nanocatalyst: [2] Synthesis of an ynone Other methods utilize an oxidative cleavage of an aldehyde , followed by reaction with a hypervalent alkynyl iodide, using a gold catalyst.
The name comes from mix of propene and argentum, which refers to the typical reaction of the terminal alkynes with silver salts. The term homopropargylic designates in the same manner a saturated position on a molecular framework next to a propargylic group and thus two bonds from an alkyne moiety. [1]
In organic chemistry, alkynylation is an addition reaction in which a terminal alkyne (−C≡CH) is added to a carbonyl group (C=O) to form an α-alkynyl alcohol (R 2 C(−OH)−C≡C−R). [1] [2] When the acetylide is formed from acetylene (HC≡CH), the reaction gives an α-ethynyl alcohol. This process is often referred to as ethynylation.
In organic chemistry, terminal alkenes (alpha-olefins, α-olefins, or 1-alkenes) are a family of organic compounds which are alkenes (also known as olefins) with a chemical formula C x H 2x, distinguished by having a double bond at the primary, alpha (α), or 1-position. [1]
The coupling of a terminal alkyne and an aromatic ring is the pivotal reaction when talking about applications of the copper-promoted or copper-free Sonogashira reaction. The list of cases where the typical Sonogashira reaction using aryl halides has been employed is large, and choosing illustrative examples is difficult.