Studies On N-nitroso-2-aryl-1, 3-oxazolidine

In this dissertation were carried out the studies on: (a) synthesis and identification of (E)-and (Z)-N-nitroso-2-aryl-1,3-oxazolidines, (b) N-nitrosation of chiral (E)-2-(benzylidene-amino) ethanols with nitric oxide, and (c) N-Nitroso-2 -aryl-1,3-oxazolidines catalyzed aromatization of Hantzsch 1,4-dihydropyridines. The principal results are listed as follows.(1) Reaction of (E)-2-(benzylideneamino)ethanol 2 with nitric oxide affords anE-rotamer dominant mixture of (E)- and (Z)-N-nitroso-2-aryl-1,3-oxazolidines 3 at room temperature in good overall yields. Two sets of ¹H,¹³C NMR peaks display 3 existing in solution as a mixture of two conformers, (E)-3 and (Z)-3. Displacement of the good leaving group nitrite (^-ONO) from N₂O₃ by the Lewis basic nitrogen of ring-2 leads to the formation of 3 (Scheme 1).The conformational isomerization of 3 was studied using density functional theory (DFT) calculations on total energies,¹H NMR chemical shifts, and equilibrium constants K for rotamers.(2) N-nitrosation of chrial (E)-(S)-2-(benzylidene-amino)ethanols 2 with nitric oxide occurs highly diastereoselctively, giving (2S,4S) diastereomer dominant N-nitroso-(2S,4S)-1,3-oxazolidines at 0℃in good yield. The N=C double bond of (E)-chain-2 is polarized to result in mostδ⁺ on the carbon atom. It favors an intramolecular nucleophilic attack of the Lewis basic oxygen on the carbon atom withδ⁺ to undergo a cycloaddition, giving an intermediate (25,45)-ring-2' with a (S) configuration at C-2 (Scheme 2). (3) A catalytic amount of N-nitroso-2-aryl-1,3-oxazolidines 2 leading to the aromatization of Hantzsch 1,4-dihydropyridines (DHPs) 1 is successfully achieved. A catalytic mechanism for the reaction is proposed. A nucleophilic attack of the nitrogen atom of 1 at the nitrogen atom of the N-nitroso of 2 most likely undergoes a transnitrosation to give a nitronium ion 4 and an oxazolidine anion 5. Followed by a proton transfer,N-nitrosodihydropyridine 6 and 7 are produced. Homolysis of 6 gives an aminyl radical 8 and NO.The 7 reacts with NO released from 6 to regenerate 2 (Scheme 3).