Synthesis of 1,2-Dihydropyridines, 2,3-Dihydro-4(1H)-pyridinone, and 1,2,3,4-Tetrahydropyridines via N-Acyl N,O-Hemiacetal Formation

✍ Scribed by Jean-Paul Roduit; Hugo Wyler

• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: German
• Weight: 830 KB
• Volume: 68
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19850680214

✦ Synopsis

Abstract

New procedures are described for the synthesis of α,β‐ethylenic and acetylenic aldehydes from 2‐butene‐ and 2‐butyne‐1,4‐diol, respectively (see Scheme 1). These are applied to the preparation of a particular δ‐acetylamino‐α,β‐ethylenic aldehyde ((E)‐5) as well as of its acetylenic analogue 15. On heating in the presence of a silyl enol ether, the former undergoes a complete dehydrative cyclization affording the N‐acetyl‐1,2‐dihydropyridine 19. The addition of HCl to aldehyde (E)‐5 results in the production of the 4‐chloro‐1,2,3,4‐tetrahydropyridine 22 which is hydrolyzed to the corresponding alcohol 23 on silica gel. Similarly, the addition of HCl or HBr to the δ‐acetyl‐amino‐α,β‐acetylenic aldehyde 15 leads to the previously unknown 4‐halo‐1,2‐dihydropyridines 26; these are easily hydrolyzed to the 2,3‐dihydro‐4(1__H__)‐pyridinone 27. The ring‐forming process involves a N‐acyl N,O‐hemiacetal as intermediate which is eventually dehydrated.