_ l-(4,5-Dimethyl-2-thiazolyl)ethanol ( 18).-Metalation of 4,5dimethylthiazole with n-butyllithium at -80°was followed by addition of a threefold excess of acetaldehyde. Isolation in the usual fashion afforded 18 in 71% yield: bp 186-188°(150 mm) [lit.21 bp 120-123°( 10 mm)]; mp 53-55°; nmr (CDClg) S 1.52 (d, 3,
The utility of o-azidostyrene derivatives as indole precursors via o-styrylnitrenes has been examined. The cyclization proceeds efficiently for /3-alkyl-and /S-aryl-o-azidostyrenes and is also satisfactory for /3-acyl-o-azidostyrenes. A synthesis of 2-acylindoles involving two steps, base-catalyzed condensation of a methyl ketone with o-azidobenzaldehyde and pyrolysis to the indole, was carried out successfully in five cases with yields from 21 to 73%. These yields are generally superior to yields of 2-acylindoles prepared by the deoxygenation method.An o-styrylnitrene would be expected to cyclize to an indole on the basis of analogy with other cyclizations of aryl azides having adjacent unsaturated substituents.2 The deoxygenation of o-nitrostyrenes to indoles may, indeed, be an example of such a cyclization.3 In view of the efficiency with which azides serve as precursors of nitrenes on thermal or photolytic decomposition,4 5a study of the synthesis and decomposition of the requisite o-azidostyrenes was undertaken.6 Particular attention was focused on 0-acyl-o-azidostyrenes because of the desirability of developing improved methods of synthesis of 2-acylindoles. Some additional studies of the deoxygenation method are also reported for purposes of comparison.
Reaction of primary aromatic amines with peroxidic tetrahydrofuran (THF) in the presence of hydrogen and 10% palladium on carbon catalyst results in THF ring opening to give 4-N-arylamino-1-butanols in good yield. The reaction mechanism is believed to involve a free-radical sequence resulting in an imino alcohol subsequently reduced to product.
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