Piperazine-2,5-dione with triethyloxonium fluoroborate

Piperazine-2,5-diones react with trimethyloxonium fluoroborate (Meer-wein s reagent) or triethyloxonium fluoroborate to generate the corresponding lactim ethers. 

The earliest report on such lactim ether formation was from Sammes [72JCS(P1)2494], who converted piperazine-2,5-dione to 2,5-diethoxy-3,6-dihydropyrazine (173) with an excess of triethyloxonium fluoroborate. Subsequently, Rajappa and Advani (73T1299) converted proline-based piperazine-2,5-diones into the corresponding monolactim ethers. The starting material was a piperazinedione in which one of the amino acid units was the secondary amino acid proline, and the other a primary amino acid. This naturally led to the regiospecific formation of a monolactim ether (169) (on O-alkylation) from the secondary amide, whereas the tertiary amide remained intact. This was later extended to piperazine-2,5-diones in which the secondary amino acid was sarcosine [74JCS(P 1)2122], leading to the monolactim ethers (170). 

Sammes and co-workers (314, 314a) have recently shown that piperazine-2,5-diones can be converted with excess triethyloxonium fluoroborate to 2,5-diethoxy-3,6-dihydropyrazines and then to 2,5-diethoxypyrazines. This reaction is discussed further in Section 6 below. 

Piperazine Derivatives. Treatment of piperazine-2,5-diones with an excess of triethyloxonium fluoroborate gives 2,5-diethoxy-3,6-dihydropyrazines (390), which can be oxidized to the parent pyrazines (391) by dichloro-cyanobenzoquinone. c/s-Diben lpiperazin ione gives a mixture of cis- and /ra j-dihydropyrazines (390). Pyrolysis of the /ro s-isomer gives 3-benzyl-2,5-diethoxypyrazine (392) in high yield with the elimination of... 

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See also in sourсe #XX -- [ ]

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