Silica compounds secondary reaction

Compound 37 was condensed with tryptamine perchlorate in the presence of sodium cyanoborohydride to provide the secondary amine 38. On the other hand, the aldehyde 37 was stirred with silica gel in methylene chloride to afford the epimer, which on reductive condensation with tryptamine perchlorate gave 39. Lactamization of 38 and 39 gave the lactams 40 and 41, respectively. Reaction of 40 and 41 with Lawesson s reagent gave the corresponding thio-lactams 42 and 43, which were treated with p-nitrobenzyl bromide to afford the crude salts 44 and 45. Reduction of 44 and 45 with sodium borohydride afforded (-)-tetrahydroalstonine (3) and (-)-ajmalicine (1), respectively. 

Dozens of reactions of free radicals (SiCla, SiClsO, Cl, OCl, H, OH, HO, =Si, =SiO, etc.), charged particles, ion-radicals, O atoms, molecules and proto-particles in the flame with SiCU, O2, H2 and related compounds on synthesis of fumed silica are worthy of special attention, since variations in synthesis conditions allow one to prepare materials strongly different in their morphological (primary and secondary particle size distributions, type of contacts between adjacent particles) and surface (concentrations of silanols and intact water) properties. These problems as well as structural and adsorptive characteristics of different silicas were analyzed in details by Mironyuk and coworkers in a series of publications [36]. 

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