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Platinum(II )-Catalyzed Isomerization of Oxo-Alkynes XI LIN 1 & ZEZHOU WANG 1 & SHIYUE FANG 1 1 Department of Chemistry, Michigan Technological University. One alkylnyl allyl alcohol was converted to the same type of allyl vinyl ether to achieve higher efficiency . Introduction.
XI LIN1 & ZEZHOU WANG1& SHIYUE FANG1
1Department of Chemistry, Michigan Technological University
One alkylnylallyl alcohol was converted to the same type of allyl vinyl etherto achieve higher efficiency
Substrate Scope Studies
Table 2. Substrate scope of Pt(II)-catalyzed isomerization of alkynylepoxidesa
Allyl vinyl ethers are valuable intermediates for the construction of highly functionalized molecules. They can undergo [3,3] sigmatropic shifts (Claisen rearrangements), due to the characteristic of forming carbon-carbon bonds in the absence of any catalysts and reagents. Allyl vinyl ethers are usually synthesized via oxygen alkylation of enolates by an allyl electrophile under strongly basic conditions, which sometimes limits the application of Claisen rearrangements.
Recently, late transition metal salts such Pt(II) halides have been found capable of acting as soft Lewis acids to activate alkynes toward nucleophilic attack. When the nucleophile is an alcohol, the product is a vinyl ether. Because such reactions are usually performed under acidic conditions, they could be used to form allyl vinyl ethers under conditions complementary to the widely used basic conditions.
The poster will report the results on the investigation of PtCl2-catalyzed isomerization of alkynyl epoxides and an alkynylallyl alcohol and the [3,3] sigmatropic shift of the resulting cyclic allyl vinyl ethers.
The resulting allyl vinyl ether products were capable to undergo [3,3] sigmatropic shifts and give piperidines as products.
Scheme 2. Claisen rearrangement of allyl vinyl ether products 2a and 2d
Optimization of Reaction Conditions
A method for the preparation of cyclic allyl vinyl ethers under acidic conditions was developed. These conditions are complementary to the normally used strongly basic conditions. The resulting allyl vinyl ether products could undergo [3,3] sigmatropic shifts to give piperidines.
Table 1. Optimization of reaction conditions for Pt(II)-catalyzed isomerization of alkynyl epoxides
The future focus will be on the synthesis of acyclic allyl vinyl ethers, and the [3,3] sigmatropic shift of the resulting products.
a Reaction conditions: substrate, PtCl2 5 mol %, toluene, reflux, 24 h
Isomerization of AlkynylAlchohol
The best yield was found in entry 3 when PtCl2 was used as the catalyst and toluene as the solvent at reflux temperature. This reaction condition was chosen for further substrate scope studies.
Department of Chemistry, Michigan Technological University;
National Science Foundation.
Scheme 1. Isomerization of an alkylnylallyl alcohol