2-Isopropyl-3,6-dimethoxy-5 - -2,5-dihydropyrazine

With chiral racemic oxiranes one enantiomer reacts faster than the other the degree of kinetic resolution is very high for L-valine/alanine-based dialkoxydihydropyrazines. For example, in the reaction of one equivalent of (2.S )-2,5-dihydro-2-isopropyl-3,6-dimethoxy-5-methyl-pyrazine (1, R1 = CH3) with two equivalents of fW-(//,/ )-2,3-dimethyloxirane (R2,R4 = CH3 R = H) virtually only the (2//,3/ )-oxirane enantiomer reacts with the lithiated dihydropyrazine to give exclusively the (l /, 2/, 2 / )-configuratcd adduct i.e., (2/ ,5S)-2,5-dihydro-5-isopropyl-3,6-dimethoxy-2-[(l/ ,2/ )-2-(2-methoxyethoxymethoxy)-l-methylpropyl]-2-methylpyrazine, entry 7. Likewise, kinetic resolution (intramolecular) occurs upon reaction with rac-7-oxabicy-clo[4.1.0]heptane (entry 8). [Pg.1051]

Isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (35, R = H) gave 2-isopropyl-3,6-dimethoxy-5-(2-methoxycarbonyl-l-phenylethyl)-2,5-dihydropyrazine (35, R = CHPhCH2C02Me) (LiBu, THF—C6H14, -70°C, 10 min then... [Pg.83]

Allyl-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (59) gave 2-allyl-2-(2-hydroxyethyl)-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (60) (BuLi, THF—C6H14, -78°C, A, 45 min then (CH2)20 [, BF3.Et20 j, -78°C, 1 h 60%).1615... [Pg.87]

C, 3 h 62%) 49 the same substrate (53) gave 2-(4-ethoxycarbonyl-l-methylbut-2-enyl)-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (62) (similarly, using MeCH=CHCH=CHC02Et >52%).218... [Pg.88]

Isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (64) gave 2-(2-acetyl-l-pheny-lethyl)-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (63) (BuLi, THF, -78°C CuBr.SMe2j, SMe2 J, -30°C, 2 h then PhCH=CHAc, 70°C, >4 h 62%)921 or 2-isopropyl-3,6-dimethoxy-5-[(4-oxocyclohex-l-enyl)methyl]-2,5-dihydropyrazine (65) (likewise, using 4-methylenecyclo-hex-2-enone 48% after separation from an isomeric byproduct).892,924... [Pg.88]

The same substrate (64) gave 2-isopropyl-3,6-dimethoxy-5-(l-methyl-2-ni-troethyl)-2,5-dihydropyrazine (66) [BuLi, THF—C6H14, 78°C, 15 min then ClTi(NEt2)3 J, 1 h then MeCH=CHN02 J, 12 h 51% this yield was lower than that (81%) obtained without titanation but the stereoselectivity was much better] also analogues.377,919... [Pg.88]

The same substrate (64) gave the complex (67) (BuLi, THF, -78°C then PhMn (CO)3.BF4 J, -78°C, 30 min 80%), and thence, by oxidative demetalation, 2-isopropyl-3,6-dimethoxy-5-phenyl-2,5-dihydropyrazine (68) [/V-bromosuc-cinimide (NBS), Et20, 20°C, 15 min 60%) also substituted-phenyl analogues likewise.169... [Pg.88]

Isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (71) and l,4-dioxaspiro[4.5]-decane-2-carbaldehyde (72) gave 2-(l,4-dioxaspiro[4.5]dec-2-yl)hydrox-ymethyl-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (73) [BuLi, THF, -70°C, 15 min then aldehyde (72) j, -70°C, 12 h 69%].521... [Pg.90]

The same substrate (71) gave 2-(l-hydroxy-l-methylethyl)-5-isopropyl-3, 6-dimethoxy-2,5-dihydropyrazine (74) (BuLi, THF—C6H14, — 70°C, 10 min the AcMe, -70°C, 1 h 98%) 196 2-(l-hydroxy-l-methylethyl)-5-isopropyl-3,6-dimethoxy-2- methyl-2,5-dihydropyrazine194 and other homologues517,905, 911 were made similarly. [Pg.90]

The foregoing chloro intermediate (80) gave a tin complex (83) that reacted with p-diethoxybenzene to afford 2-(2,5-diethoxyphenyl)-5-isopropyl-3, 6-dimethoxy-2,5-dihydropyrazine (84) (EtOC6H4OEt-p, SnCl4, CH2C12 then (80) i, —78°C, 6 h 65%).920... [Pg.91]

Allyl-5-isopropyl-3,6-dimethoxy-2-(prop-2-ynyl)-2,5-dihydropyrazine (315) gave a separable mixture of 8-isopropyl-7,10-dimethoxy-2,3-dimethylene-6, 9-diazaspiro[4.5]deca-6,9-diene (316) and 3-isopropyl-2,5-dimethoxy-10-methylene-l,4-diazaspiro[5.5]undeca-l,4,8-triene (317) [Pd(OAc)2, PPh3, PhH, A, 20°C, 24 h 32 and 24%, respectively, after separation] also analogous reactions.1610... [Pg.127]

Chloroethyl)- gave 2-(2-bromoethyl)- (NaBr, Me2NCHO, 70°C, 12 h 88%) or 2-(2-iodoethyl)-5-isopropyl-3,6-dimethoxy-2-methyl-2,5-dihydropyrazine (likewise but Nal 88%).1608... [Pg.181]

Bromomethyl-5-isopropyl-3,6-dimethoxy-2-methyl-2,5-dihydropyrazine (272) gave 2-isopropyl-3,7-dimethoxy-6-methyl-2//-diazepine (273) and/or the isomeric 2-isopropylidcnc-3,7-diincthoxy-6-methyl-5,6-dihydro-2//-diazcpinc (274) [Bu OK, Mc2SO, 50°C, 1 h 0 and 75%, respectively KOH, Me2SO, 25°C, 24 h 73% and 6%, respectively KOH, Mc2SO, 50°C, 5 h 93% and trace, respectively the kinetics and mechanism have been studied].923... [Pg.189]

Allyl-2-(2-hydroxyethyl)- (137, R = CH2OH) gave 2-allyl-2-formylmethyl-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazine (137, R = CHO) [Me2SO, (COCl)2, CH2C12, 60°C, A, 5 min then substrate J, - 60 — - 15°C,... [Pg.212]

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