Bolourtchian, S M

Heravi, M M

Mojtahedi, M M

NOPR

Indian Journal of ChemistryVol. 378. June 1998, pp 590 - 592Claisen rearrangment of 3-(prop-2-ynylsulfanyl)-1,2,4-triazinone:A convenient route to 2-methyl-thiazolo[3,2-b][I,2,4]triazinoneM M Heravi*, M M Mojtahedi & S M BolourtchianChemistry and Chemical Enginnering Research Center of Iran,P.O.Box: 14335-186, Tehran-Iran, Fax (21)8037185Received 4 August 1997; accepted (revised) 24 March 19986-Methyl-3- (prop-2-ynylsulfanyl)-I,2,4-triazin-5(2H)-one 1 on refluxing with hexamethyl phophoric triamide(HMPT), in the presence of catalytic amount ofPdCI2(PhCN)2 affords 2,6-dimethylthiazolo [3,2-b][1,2,4] triazin-7-one 10 via an interesting Claisen rear-rangment. This structure has been confirmed by unambi-guous synthesis of 10.Palladium catalyzed S~N allylic rearrangment ofallylsulfanyl pyrimidinone and allylsulfanyl-I,2,4-triazinone have been studied extensively owing totheir synthetic utility'<. However examples ofS~N propynylic rearrangments are very scarce.The S~N propynylic rearrangment of 2-(prop-2ynylsulfanyl) benzimidazole is typical example':".Recently we have demonstrated that base' andPd_salt6,7 very effectively catalyze the cyclizationof prop-Z-ynylsulfanyl-Lz.a-triazinone to corre-sponding 3-substituted thiazolo [1,2,4] triazinone.In this pattern of cyclization and aromatization andother methods '" to synthesize thiazolotriazine,only 3-substituted thiazolo [1,2,4] triazinone canbe obtained. Here we wish to report two independ-ent routes to synthesis 2,6-dimethylthiazolo [3,2-b][1,2,4] triazin-7-one 10.6-Methyl-3(prop-2-ynylsulfanyl)-1,2,4-triazin-5-one 1 was refluxed in HMPT with catalytic amountof Pd Ch(PhCN)2 for 32 hrs. After evaporation ofsolvent under reduced pressure, the crude materialwas subjected directly to column chromatorgraphyto obtain a crystalline compound as a majorproduct.Taking into consideration the problem of regio-chemistry, first we thought of alkylation at the N-2vs. N-4, by direct nucleophilic addition of amide toNote3 45 6~syN"foHN""'N~Me70~N'yON""'N~Me8acetylenic moiety and subsequent isomerization ofeither intermediate 2 or 3 to either 4 or 5 respec-tively. This pattern of cyclization and isornerizai-ton by base has been noticed previously". Compari-son of spectroscopic data of obtained compoundwith those known 45 and 57 showed considerabledifferences. Therefore we considered thermal andcatalyzed [3,3] sigmatropic rearrangment of 1 toeither 6 or 7 with the subsequent cyclization to ei-ther 8 or 9 followed by isomerization to either 10or 11 respectively. (Scheme I).INDIAN J CHEM, SEC.B, JUNE 1998 591HMPT •PdCI 2(PhCN) 2or 11 _ 810Scheme ITo prove this pattern of one pot [3,3] sig-matropic shift, cyclization and isomerization wedecided to synthesize 2-substituted thiazolotriazi-none 10 or 11 unambiguously.6-Methyl-3-thioxo-l,2,4-triazin-5-one 12 wasrefluxed with excess of hexamethyl disilazane(I·IMOS) and a catalytic amount of (NI-Lt)2S0410and thereafter propynylbromide was added. Afterusual work-up a single (TLC) compound was iso-lated in fairly good yield which could be either 6 or7.The corresponding N-propynyl compound 6 or 7was cyclized and isomerized by acid catalysis!'. toafford the identical compound which was obtainedby refluxing 1 with HMPT (10 or 11) (Scheme II).The structure 10 or 11 was carefully discriminatedby the comparison of its UV spectrum with thoseof well established 4 (Xmax 280 nm)' and 5 «max298 nm)'. 3,4-0isubstituted-l,2,4-triazin-5 onesare known to show the absorption maxima at thelonger wavelenghts compared to 2,3-disubstitutedcompounds" 5 also showed the absorption maximaat the longer wavelength compared to 4. The UVspectrum of compounds 10 or 11, was quite similarto that of 4. Therefore we concluded that in S~ Npropynylic rearragment in HMPT, the propynylicgroup migrates to N-2 of 1,2,4-triazine regioselec-tively to afford 6 which subsequently cyclizes andisomerizes to 10. N-Alkylation of 1,2,4-triazine 12in the presence of HMOS also occures on N-2 se-lectively, leading to 2-propynyl derivative 6. Acidcatalyzed cyclization and isomerization of the lat-ter led to 10.6 or 7Ior 9IIMUS----- ----+(NH.) ,so.r=>Br11 or 7orScheme IIExperimental SectionMelting points were obtained on a Buchi 530and are uncorrected. IHNMR spectra were re-corded in 8 ppm a Brucker Ac 80 spectrometer indimethyl sulfoxide as solvent using TMS as inter-nal standard. IR spectra were recorded on a Perkin-Elmer model 883 using KBr disk and mass spectraon a Varian CH-7.2,6-Dimethyl thiazolo [3,2-h1[I,2,4] triazin-7-one lO-Compound 1 (lg,55 mmoles) andPdCh(PhCN)2 (O.lg) were refluxed in HMPT (20mL) for 32 hr. The solvent was evaporated off invacuo. The crude mixture was washed with waterand extracted with chlorofom. This solution wasdried over anhyd. Na2S04 and evaporated off. The592 INDIAN J CHEM, SEC.B, JUNE 1998residue obtained was subjected to column chro-matography using CHCh: MeOH, 90:10 to affordthe title compound. Yield 0.38g, (38%), m.p.168-69°; IHNMR (CDCh): 02.38(s,6H,2Me),6.43(s,lH,CH of thiazole ring). IR: (KBr): 3420,2928, 1640 (amide carbonyl), 1489 and 1372 em";UV (CHCh): (/.. max 282 nm. M.S: rn/z, ~,181(25), 180(55), 156(18), 139(100), 72, 40(95).6-Methyl-2N-Propynyl-3-thioxo-l,2,4-triazin-S-one 6. 6-Methyl-3-thioxo-l,2,4-triazin-S-one12-{0.36g, 2.5 mmoles), was refluxed with hex-amethyldisilazane (HMDS) (0.7 mL, excess) and acatalytic amount of (N~)2S04 (12.5 mg) until adear solution was obtained. Excess HMDS wasremoved by disitlation in vacuo. The catalyticamount of 12 and propynyl bromide (O.l8g, 1mmole) in CH3CN (5 mL) was added and the reac-tion mixture' was refluxed for further 4 hr. Afterevaporation of solvent in vacuo, the residue wastreated with water to afford the spectroscopic pureproduct. Yield (0.4 g, 93%), m.p. 98-99°; IHNMR(DMSO-~): 02.1(s,3H,Me), 3.l(t,IH,-C-CH,J=2.lHz), 3.95 (d, 2H, CH2, J=2.l Hz); IR: (KBr):3417, 3258, 2928, 1640, 1590, 1459, 1033 em";M.S: rn/z, ~, 181(22), 143(18), 140(85), 72(100),71(75),80(90),55(65).Acid catalyzed cyclization of 6 tolO---Compound 6 (0.25g, 1.38 mmole) was dis-solved in cone H2S04. The reaction mixture waskept at 50 C for 5 hrs. It then poured onto crushedice and the solution was neutralized by addingNaOH. The precipitated solid was crystallizedfrom EtOH to afford spectroscopic pure 10. Yield0.175g, (70%), mp 168-69.References1 Mizutani M, Sanemitsu Y, Tamaru Y & Yoshida Z,J.Org.Chem, 48, 1983,4585.2 Mizutani M, Sanemitsu Y, Tamaru & Yoshida Z, Tetrahe-dron, 1984,5289.3 Balasubramanian K K & Venligopalan B. Tetrahedronleft, 1974,2643.4 Balasubramanian K K & Venligopalan B. Tetrahedronleft, 1974,2645.5 Heravi M M, Iran.J.Chem & Chem Eng, 11(2),1992,8.Chemical Abstract, 120-323500d.6 Heravi M M & Bakavo1i M., J.Chem.Res, 11,1995,480.7 Heravi M M, Bakavoli M, Shafaie M, Sadeghi M M &Khoshdast A, Indian. J.Chem.. 35,1996,1260.8 Nyitrai J, Bekassy S & Lempert K. Acta Chem AcadSci.Hurg, 53,1967. 309.9 Dawnis J, Guindio Y, Jacquier R & Viallefont P,Bull.Soc.Chim.Fr, 1972, 1511.10 Muller C E, Tetrahedron u« 32(45), 1991,6539.11 Heravi M M, Aghapoor K & Nooshabadi M H tosynth commun, 28(2), 1998 in Press.

Claisen rearrangment of 3-(prop-2-ynylsulfanyl)-1,2,4-triazinone: A convenient route to 2-methylthiazolo[3,2-b][I,2,4]triazinone

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Claisen rearrangment of 3-(prop-2-ynylsulfanyl)-1,2,4-triazinone: A convenient route to 2-methylthiazolo[3,2-b][I,2,4]triazinone

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