1,2-Propargylic rearrangement

When X=OH, this conversion of acetylenic alcohols to unsaturated aldehydes or ketones is called the Meyer-Schuster rearrangement The propargyl rearrangement can also go the other way that is, 1-haloalkenes, treated with organocopper compounds, give alkynes. ... 

The propargyl rearrangement in which the incoming anion and outgoing anion are different is called a displacement (Eq. 48). Some examples are summarized in Scheme 2. 

Thermal propargyl rearrangement-Claisen rearrangement of propargyl vinyl ethers and Cope-type rearrangements of propargyl malonates [93]. 

The transformation termed propargylic rearrangement attracted much attention, and detailed discussions are available in review papers.134-141 Suitable reagents to bring about this rearrangement are metal alkoxides and metal amides in alcohols and dipolar aprotic solvents (DMSO, HMPT), and metal amides in ammonia. Reactivities are strongly dependent on the base employed, the solvent, and the reaction conditions. 

Considering the thermodynamic stability of isomeric acetylenes and dienes 1,3-dienes, by far the most stable compounds involved in propargylic rearrangements should be formed in the highest amount. They are, however, rarely observed since they are formed in a slow reaction. The product distribution, consequently, is kinetically controlled. 

Similar to the base-catalyzed double-bond shift of alkenes, the question of intra-molecularity arises in the propargylic rearrangement as well. Intramolecularity was... 

While this was a noble and worthwile goal, it was not at all easy. Thus where planned strategies ended in frustration, serendipity suddenly intervened. Propargylic bromide was found to react with phenothiazine leading to the first ynamine via an unexpected propargylic rearrangement (Eq. 62)109). This was in 1958 and the structure proof based only on IR evidence and add hydrolysis has elicited a certain incredulity. 

The rather basic lithiated secondary amines may give rise to another kind of side-reactions e.g. isomerisation of ynamines into aminoallenes (see Propargylic Rearrangements)... 

It can be concluded that propargylic rearrangements make an excellent and expeditious method of access to various 2-methyl ynamines, their vinylogs and ethynylogs. 

Phosphaallenes can be synthesized in the same way as 1,3-diaryl-substituted allenes following an aluminium-catalyzed propargyl rearrangement. Using sodium hydroxide-activated aluminium oxide (125), the synthesis is suitable on an enlarged scale without any detectable by-products [Eq. (63)]. A similar proton migration within a coordinated phosphaalkyne was reported recently (126). 

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