Sulfoxide alkylation

An unusual one-pot intramolecular sulfoxide alkylation-elimination reaction was found by Gibson et al. <2001SL712>. These authors found that treatment of 459 with potassium bis-trimethylsilylamide resulted in a ring closure to 460 in acceptable yield. Furthermore, Batori and Messmer found an effective method for preparation of [l,2,3]triazolo[l,5- ]pyrimidinium salts <1994JHC1041> oxidative cyclization of hydrazones 461 by 2,4,4,6-tetrabromo-2,5-cyclohexadienone gave rise to the quaternary salts 462. Under certain reaction conditions, the formation of 6-bromo-salts 462 (R6 = Br) was also experienced. As neither the starting compound nor the quaternary triazolopyridinium salt underwent bromination in this position, the authors assumed that this bromination process occurred on one of the intermediates in the course of the above-mentioned cyclization reaction. 

The impact of electron donor ligands in NdX3-systems has already been discussed in Sect. 2.1.1.1. ligands such as alcohols, trialkyl phosphates, alkyl sulfoxides, alkyl amides, THF, N-oxides, pyridine etc. are added in order to facilitate water removal from NdCl3 6H20 by azeotropic distillation and in order to increase solubility and activity of NdCl3-based catalyst systems in organic solvents. 

S—O Stretching Vibrations Sulfoxides Alkyl and aryl sulfoxides as liquids or in solution show strong absorption in the 1070-1030 cm 1 region. 

This synthesis involves some stereochemistry. Biotin carries the alkyl chain next to sulfur on the more hindered endo face of the molecule, and any successful synthesis has to address this particular problem. Here, the chemists decided to use the fact that alkylations of cyclic sulfoxides result in tram stereochemistry between the new alkyl group and the sulfoxide oxygen atom. As expected, oxidation of the sulfide proceeded faster from the exo face, giving an 8 1 ratio of exoiendo sulfoxides. Alkylation trans to the exo oxygen gave the desired (endo) product. 

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