Ring synthesis 7-hydroxy-2,4-dimethyl

The DE ring of camptothecin has been prepared enantioselectively in six steps from 2-fluoropyridine using a halogen dance reaction <95TL(36)7995>. The first total synthesis of dimethyl sulfomycinamate (47) was reported starting from 3-hydroxy-6-methylpyridine (48) <95TL(36)5319>. 

H-Benzo[a]carbazole, 4,4a,5,l 1,1 la,l Ib-hexahydro-synthesis, 4, 283 Benzo[b]carbazole, N-acetyl-photochemical rearrangements, 4, 204 Benzo[/]chroman-4-one, 9-hydroxy-2,2-dimethyl-synthesis, 3, 851 Benzochromanones synthesis, 3, 850, 851, 855 Benzochromones synthesis, 3, 821 Benzocinnoline-N-imide ring expansion, 7, 255 Benzocinnolines synthesis, 2, 69, 75 UV, 2, 127 Benzocoumarins synthesis, 3, 810 Benzo[15]crown-5 potassium complex crystal stmcture, 7, 735 sodium complex crystal stmcture, 7, 735 Benzo[ 18]cr own-6 membrane transport and, 7, 756 Benzo[b]cyclohepta[d]furans synthesis, 4, 106 Benzocycloheptathi azoles synthesis, 5, 120... 

Pyrazolino[2,3-c][l,2,3]triazoles, 5, 702 Pyrazolium hydroxide, l,2-dimethyl-3,5-diphenylanhydro-4-hydroxy-IR spectra, 5, 201 Pyrazolium salts dequatemization, 5, 269 H NMR, 5, 185 hydrogen exchange at ring carbon, 5, 245 mesoionic compounds, 5, 171 nitrodebromination, 5, 237 reactivity, 5, 217 reduction, 5, 68, 243 synthesis, 5, 156 UV spectra, 5, 199 Pyrazolium salts, amino-reactions, 5, 262 Pyrazolium salts, bromo-nucleophilic displacements, 5, 266 Pyrazolium salts, 1,2-dimethyl-deuteration, 5, 175, 245 hydrogen exchange, 5, 71 acid-catalyzed, 5, 239 reactions... 

Partly saturated pyrazino[l,2-r-]pyrimidines were prepared by formation of the pyrazine ring. 2-Substituted-8-hydroxy-3,4-dihydro-177,277-pyrazino[l,2-r-]pyrimidin-l-ones were prepared by a [6+0] synthesis involving cyclization of 6-hydroxy-pyrimidine-4-(fV-hydroxyethyl)carboxamides <2005W02005/087766>. The 2/7-pyra-zino[l,2-c]pyrimidine-3-carboxamide 164 (Y = NH) was formed from [5+1] atom fragments via the uracil derivative 163 (Y = NH) and DMF-dimethyl acetal. Compounds 163 were prepared from 6-chloromethyluracil and glycine methyl ester 162 (Y = NH) (Scheme 20) <2004W02004/014354>. 

Examples of 5-exo cyclizations in which the hydroxy group is constrained by a five-membered ring are shown by equation (53). The stereoselectivity in these cyclizations ranges from quite high in iodocy-clization (9 1 in H2O and >20 1 in CH2CI2) to only moderate (2—3 1) with mercury and phenylselenenyl chloride. P This type of cyclization has been widely applied to synthesis of prostacyclins.146 Similar cyclizations with dimethyl(methylthio)sulfonium fluoroborate have been reported recently.35... 

Also, the primary amine moities of polar lipids catalyze the aldol condensation of Cm-Cig aldehydes resulting from plasmalogen hydrolysis, thus forming a,3-unsaturated aldehydes (l2t). Phosphatidyl ethanolamine reacted with propanal and n-hexanal forming phosphatidyl l-(2-hydroxyethyl)-2-ethyl-3,5-dimethyl pyridinium, and phosphatidyl-1-(2-hydroxy ethyl)-2-hexyl-3,5-dipentyl pyridinium, respectively (125). The peridinium ring is formed by the reaction between one mole of amino-N of phosphatidyl ethanolamine and three moles of n-alkanals. The same reaction took place in the synthesis of substituted pyridines by condensation of carbonyl compounds with ammonia (126, 127). 

Direct ring syntheses are also available for the preparation of hydroxypyrazines. Thus, haloacylation of an a-aminoketone, followed by reaction with ammonia and oxidation represents a general synthesis of 5,6-disubstituted and 3,5,6-trisubstituted 2-hydroxypyrazines.339 This is illustrated by the preparation of 5,6-dimethyl-2-hydroxy-pyrazine (Scheme 39). Hydroxypyrazines are very conveniently... 

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