Hydrogenation of ß-Keto Sulfones to ß-Hydroxy Sulfones with Alkyl Aluminum Compounds: Structure of Intermediate Hydroalumination Products.

ß-Hydroxy sulfones are important in organic synthesis. The simplest method of ß-hydroxy sulfones synthesis is the hydrogenation of ß-keto sulfones. Herein, we report the reducing properties of alkyl aluminum compounds R3Al (R = Et, i-Bu, n-Bu, t-Bu and n-Hex); i-Bu2AlH; Et2AlCl and EtAlCl2 in the hydrogenation of ß-keto sulfones. The compounds i-Bu2AlH, i-Bu3Al and Et3Al are the at best reducing agents of ß-keto sulfones to ß-hydroxy sulfones. In reactions of ß-keto sulfones with aluminum trialkyls, hydroalumination products with ß-hydroxy sulfone ligands [R2AlOC(C6H5)CH2S(O)2(p-R1C6H4]n [where n = 1,2; 2aa: R = i-Bu, R1 = CH3; 2ab: R = i-Bu, R1 = Cl; 2ba: R = Et, R1 = CH3; 2bb: R = Et, R1 = Cl] and {[Et2AlOC(C6H5)CH2S(O)2(p-ClC6H4]∙Et3Al}n3bb were obtained. These complexes in the solid state have a dimeric structure, while in solutions, they appear as equilibrium monomer-dimer mixtures. The hydrolysis of both the isolated 2aa, 2ab, 2ba, 2bb and 3bb and the postreaction mixtures quantitatively leads to pure racemic ß-hydroxy sulfones. Hydroalumination reaction of ß-keto sulfones with alkyl aluminum compounds and subsequent hydrolysis of the complexes is a simple and very efficient method of ß-hydroxy sulfones synthesis.