Hexacarbonylmolybdenum-induced Reaction of 2-lsoxazolines Formation of Pyridine Derivatives

Abstract

The reaction of 3-aryl-5-phenyl-2-isoxazoline [15] with [Mo(CO)₆] (Equation ( 5 ), Table 1) follows two pathways both via an intermediate of the pentacarbonyl(2-isoxazoline-N)molybdenum ( 0 ) species [21] (Scheme 1). One includes the N-O bond cleavage and subsequent reactions to result in the formation of 1-aryl-3-phenyl-1-propanone [17], 1-ary1-3pheny1-2-propen-1-one [18], and 1, 3-diary1-5, 8-diphenyl-2, 6-diazabicyclo[2.2.2]oct-3-ene [19]. The other pathway includes the N-O and C4-C 5 bond cleavages to give benzaldehyde [20] and (1-arylvinyl) nitrene complex [2]. The reduction-hydrolysis and dimerization of [2] give acetophenone derivative [4] and 2, 5-diarylpyrrole [3], respectively. Furthermore, [2] undergoes novel cyclocondensation with 1-aryl-3-phenyl-2-propen-1-one [18] to give 2, 6-diaryl-4-phenylpyridine [16] (Scheme 2). Evidence for the mechanistic aspect of the formation of the pyridine is obtained by the studies on the [Mo(CO)₆]-induced reaction of a-azidostyrene [1a] with α, β-unsaturated ketones [18a] and [18c-d] (Table 2). The reaction of 3-hydroxy-1, 3-diphenyl-1-propanone oxime [35] with [Mo(CO)₆] was also found to give 2, 4, 6-triphe nylpyridine [16a] in a similar manner (Equations ( 6 ) and ( 7 )).