Unexpected cleavage of the N–N bond in the reactions of 3-pyrazolidinone-1-azomethine imines with HCN

1,3‐Dipolar cycloadditions of (4R*,5R*)‐1‐alkylidene‐4‐(benzoylamino)‐5‐phenyl‐3‐pyrazolidinon‐1‐azomethine imines

“…Most probably, isolation of isomerically pure cycloadducts was due to the loss of the other isomer(s) during isolation rather than due to the high stereoselectivity of cycloadditions. Stereocontrol of cycloadditions seems analogous to that, observed previously in cycloadditions to their orthounsubstituted 1-arylmethylidene analogues [20][21][22], i.e. approach of dipolarophiles took place predominantly from the less hindered face of dipoles 3, cycloadditions of methyl acrylate (5) and dimethyl maleate (6) were endoselective, whilst cycloadditions of N-phenylmaleimide (8) were exo-selective.…”

“…On the other hand, isolation of single diastereomers 9, 10a, and 13a,b-16a,b could be explained by the loss of the minor isomer(s) during chromatographic or crystallization workup. By analogy with cycloadditions of 1-arylmethylidene analogues [13,[20][21][22] it could be presumed, that preferential approach of dipolarophiles 4-8 took place from the less hindered face of dipoles 3a,b. The structures of the isolated cycloadducts 13, 14, and 16 indicate, that stereocontrol of these cycloadditions was analogous to that, observed previously in reactions to their orthounsubstituted 1-arylmethylidene analogues [20,21]: cycloadditions of methyl acrylate (5) and dimethyl maleate (6) The structures of novel compounds 3b, 9, 10a, 10/10'b, and 13a,b-16a,b were determined by spectroscopic methods (ir, 1 H and 13 C nmr, NOESY spectroscopy, and ms) and by elemental analyses for C, H, and N. Compound 13a was not obtained in analytically pure form.…”

“…Asymmetric cycloadditions in chiral nitrone, nitrile oxide, and azomethine ylide series are well elaborated, however, much less examples have been reported in chiral azomethine imine series [1][2][3][4]. Stable chiral azomethine imines have been prepared from pyridazine-diazoalkane cycloadducts [5][6][7][8][9], 3-pyrazolidinones [10][11][12][13][14][15][16][17][18][19][20][21][22], and 1,3,4oxadiazin-2-ones [23][24][25][26]. Generally, 1,3-dipolar cycloadditions of such cyclic chiral azomethine imines to various dipolarophiles were accompanied by high facial and endo/exo-selectivity and afforded the corresponding functionalized fused pyrazolones with a bridgehead N-N structural element .…”

“…In the last decade, a part of our research interest has also been devoted to the chemistry of 3-pyrazolidinones and their fused analogues [13][14][15][20][21][22]31,32]. In this connection, we have previously reported 1,3-dipolar cycloadditions of (1'Z,4R*,5R*)-1-(arylmethylidene)-4-(benzoylamino)-5-phenyl-3-pyrazolidinon-1-azomethine imines to various dipolarophiles.…”

“…In this connection, we have previously reported 1,3-dipolar cycloadditions of (1'Z,4R*,5R*)-1-(arylmethylidene)-4-(benzoylamino)-5-phenyl-3-pyrazolidinon-1-azomethine imines to various dipolarophiles. The regiochemistry and stereochemistry of these cycloaddition reactions was controlled by the stereodirecting group in chiral dipole, by the orthosubstituents at the aromatic ring, and by the structure of the dipolarophile [13,[20][21][22]. In contrast to 1-arylmethylidene substituted 3-pyrazolidinone-1-azomethine imines, 1,3-dipolar cycloadditions of 1-alkylidene substituted analogues have not been studied yet.…”