1.1- dicyano-2-methoxycarbonyl

Unsymmetrical dienes in this synthesis are often capable of high regioselectivity (eqs. 4 and 5) (82). Reaction of (81) with 2-methoxycarbonyl-l,4-ben2oquinone [3958-79-0] yields 97% of (82) [80328-15-0]. Reaction of (81) with 2,3-dicyano-l,4-ben2oquinone [4622-04-2] yields 58% of (83) [80328-16-1]. 

Dicyano-3,6-dimethylpyrazine shaken with sodium ethoxide at room temperature for 10 hours produced 2-cyano-5-ethoxy-3,6-dimethylpyrazine (288). Bromination of 2-methoxy-3-sulfanilamidopyrazine (39) in methanol led to 5-(4 -amino-3, 5 -dibromobenzenesulfonimido)-6-hydroxy-2,3-dimethoxy-2,3,4,5-tetrahydropyrazine (32) which with 2 N sodium hydroxide gave 3-(4 -amino-3, 5 -dibromobenzenesulfonamido)-2-hydroxy-5 nethoxypyrazine (40) (816). The preparation of 2-amino-3,5-dicyano-6-methoxy(and ethoxy)pyrazine from a-(p-toluenesulfonyloxyiminomalononitrile and malononitrile has been described in Section II.7 (484). 2-Methoxycarbonyl(and cyano)-5-pyridiniopyrazine chloride (41) is reported (conditions not stated) to give 2-carboxy(and carbamoyl)-5-methoxypyrazine (765). 

Heating of l,4-dicyano-2,3-dinitroso-2,3-diphenylpiperazine ( ) (1572, cf. 1573) in mesitylene is claimed to give l,4-dicyano-2,3-diphenyl-1,4,5,6-tetrahydro-pyrazine (1572), and l-carbamoyl-3-hydroxy-2,3-diphenylpiperazine ( )(1572, cf. 1573) with methyl iodide and potassium carbonate in methanol is claimed to give 4-carbamoyl-l,l-dimethyl-2,3-diphenyl-l,4,5,6-tetrahydropyrazinium iodide (1572). 2-Diethylamino-l,4-dimethylpiperazine on thermal treatment gives 1,4-dimethyl-l,2,3,4-tetrahydropyrazine, which was methoxycarbonylated to 5-methoxycarbonyl-1,4-dimethyl-l, 2,3,4-tetrahydropyrazine (1593). 

Abbreviations Ac acetyl AIBN azobisisobutyronitrile All allyl Bn benzyl Bz benzoyl ClAc chloroacetyl DAST diethylaminosulfur trifluoride DBU l,8-diazabicyclo[5.4.0]-undec-7-ene DDQ 2,3-dichloro-5,6-dicyano-/)-benzoquinone DMDO dimethyldioxirane DMTST dimethyl(methylthio)sulfonium trifluoromethanesulfonate Fmoc 9-fluorenyl-methoxycarbonyl HDTC hydrazine dithiocarboxylate IDCP iodonium di-collidine perchlorate Lev levulinoyl MBz 4-methylbenzoyl Me methyl MEK methyl ethyl ketone MP 4-methoxyphenyl NBS iV-bromosuccinimide NIS A-iodosuccinimide Pent n-pentenyl Pfp pentafluorophenyl Ph phenyl Phth phthaloyl Piv pivaloyl PMB 4-methoxybenzyl TBAF tetrabutylammonium fluoride TBDMS tcrt-butyldimethylsilyl TBDPS tert-butyldiphenylsilyl TCA trichloroacetyl TES triethylsilyl Tf trifluoromethanesulfonyl TMS trimethylsilyl Tol 4-methylphenyl Tr trityl Troc 2,2,2-trichloroethoxycarbonyl Ts tosyl. 

Bis-[4-methoxy-phenyl]-2-cyclopropenyliden)-9-(dicyano-methylen)-9,10-dihydro- 2975 2(or 3)-Chloromethyl- 2879 lO-Deuterio-9-methoxycarbonyl- 2880 1 -Hy droxy-7-methoxy-1 -(1 -phenylthio-cy clo-propyl)-l,2,3,4-tetrahydro- 1480 9-Melhoxycarbonyl- 2888 7-Methoxy-l-(l-phenylthio-cyclopropyl)-3,4-dihydro- 1480 9-Methyl- 2048... 

As mentioned above, thieno[3,4-c]thiophene is most difficult to synthesize compared to all other isomeric thienothiophenes. A few of its derivatives are known tetraphenyl- (67JA3639, 73JA2558, 73JA2561), tetrakis(alkylthio)- (85JA5801), tetra(2-thienyl)- [42], tetrabromo-, l,3-dibromo-4,6-dicyano-, l,3-dibromo-4,5-bis (methoxycarbonyl)- (94JOC2223), l,4-bis(rert-butylthio)-3,6-diphenyl- and 3,6-di (2-thienyl)thieno[3,4-c]thiophenes (98JOC163). 

Fowler, F. W. Cycloadditions of N-methoxycarbonyl-2,3-homopyrrole . Angew. Chem. 1971, 83, 148-149. Angew. Chem. Int. Ed. Engl. 1971,10, 135-136. Baldwin, J., Pinschmidt, R. K. jr. The Cycloaddition of Bicyclo2.1.0pent-2-ene with Tetracyanoethylene . Tetrahedron Lett. 1971, 935-938. Christl, M., Brunn und E., Lanzendoerfer, F. Reactions of Benzvalene with Tetracyanoethylene,2,3-Dichloro-5,6-dicyano-p-benzoquinone, Chlorosulphonyl Isocyanate, and Sulphur Dioxide. Evidence for Concerted 1,4-Cycloadditions to a Vinylcyclopropane System . J. Am. Chem. Soc. 1984,106, 373-382. 

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