Amine with propargyl vinyl ethers

We attempted the synthesis of 1,2-dihydropyridines from propargyl vinyl ethers in an independent study (11JOC2145). In our early experiments, we studied propargyl vinyl ethers 79 with additional alkyl substituents at the vinylic position. The propargyl Claisen rearrangement was effected by catalytic amounts of silver(I) hexafluoroantimonate, and the addition of an amine to the aUenylcarbonyl intermediate was expected to provide the 1,2-dihydropyridine product 80. Unfortunately, the major product was, in aU cases, the 2ff-pyran 81, and the desired dihydropyridine 80 was only formed in yields ranging from 10% to 44% when aniline derivatives were employed (Scheme 27).With aliphatic amines, the formation of 1,2-dihydropyridines was not observed. 

On the other hand, propargyl vinyl ethers 82 with no additional substituent at the vinylic position were smoothly converted into 1,2-dihydropyridines 85 (Scheme 28). While the initial rearrangement was catalyzed best by the action of gold(I) chloride instead of silver(I) hexafluoroantimonate, the sequential addition of an amine and 20mol% of p-toluenesulfonic acid... 

Kirsch has reported the conversion of propargyl vinyl ethers to form pyrroles via a multi-step transformation involving the silver-catalyzed propargyl Claisen rearrangement to form the a-allenyl P-keto ester, condensation with a primary aryl amine. 

REPPE PROCESS. Any of several processes involving reaction of acetylene (1) with formaldehyde to produce 2-butync-l,4-diol which can be converted to butadiene (2) with formaldehyde under different conditions to produce propargyl alcohol and, form this, allyl alcohol (3) with hydrogen cyanide to yield acrylonitrile (4) with alcohols to give vinyl ethers (5) with amines or phenols to give vinyl derivatives (6) with carbon monoxide and alcohols to give esters of acrylic acid (7) by polymerization to produce cyclooctatetraene and (8) with phenols to make resins. The use of catalysis, pressures up to 30 atm, and special techniques to avoid or contain explosions are important factors in these processes. 

This hypothesis has been verified starting from (Z)-y-iodoallyl ethers [109], amines [107], and thioethers [107] (Scheme 7-95) that are easily accessible from a propargyl ether [110] or ethyl propiolate [111]. In each case, the heteroatom chelates the vinylmetal to form a rigid five-membered ring and the allyl moiety approaches the vinyl one with a diastereofacial selectivity anti to the alkyl group [112]. 

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