Nitriles in Heterocyclic Synthesis: Novel Synthesis of

Nitriles in Heterocyclic Synthesis: Novel Synthesis of 4H-Thiopyran and of 2-Hydroxy-6-pyridine Thione Derivatives Galal Eldin Ham za Elgem eie, Sherif Mourad Sherif, Fatma A bd El M aksoud A bd El A al, and M oham ed Hilmy Elnagdi* D epartm ent of Chem istry; Faculty of Science; Cairo University, Giza, A. R. Egypt Z. N aturforsch. 41b, 781-783 (1986); received January 20, 1986 C yanothioacetam ide, 2-Aminothiopyrans, Pyridine Thiones, 13C NM R Spectra Reaction of arylm ethylenem alononitrile 2 a —c with cyanothioacetam ide 1 afforded 4-aryl-2,6diam ino-4H -thiopyran-3,5-dicarbonitriles 5 a —c on refluxing in ethanolic aqueous triethylam ine, rearranged to yield the 4-aryl-l,2-dihydro-6-hydroxy-2-thioxo-3,5-pyridine dicarbonitriles 8 a —c. The same com pounds could be obtained on treatm ent of 2 a —c with 1 in ethanolic aqueous triethylam ine or on reacting 1 with 2 d —f. The 13C NM R data of the products are reported and interpreted.

In the last few years we were involved in the prep­ aration of polysubstituted heterocycles starting with readily obtainable nitriles [1—3]. A s a part of this program we investigated the reaction of cyano­ thioacetam ide 1 with the cinnamonitriles 2 a —f. In the last decade, reports have appeared describing the reaction of 2 with active m ethylene reagents that af­ forded either pyran or pyridine derivatives [4—8]. In our laboratory it has been found that 1 reacts with 2 a —c to yield 1:1 adducts. The same products were obtained on reacting m alononitrile with the a-cyanocinnam othioacetam ides 3 a —c. This finding indicated that the reaction of 1 with 2 a—c proceeds via initial addition of the active m ethylene m oiety in 1 to the activated double bond in 2 thus forming either the acyclic M ichael adducts 4 a —c or their cyclization products 5 or 6. ‘H N M R spectra fit the thiopyran form 5 but can scantly be interpreted in favour of the dihydropyridine 6 in the tautomeric form 7. The 13C N M R spectrum established the thiopyran struc­ ture 5. Thus, in addition to aryl carbons (and the methoxycarbon in case of reaction of 1 with 2 b) 13C N M R showed four signals at