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

β-Hydroxy sulfones are important in organic synthesis. The simplest method of β-hydroxy sulfones synthesis is the hydrogenation of β-keto sulfones. Herein, we report the reducing properties of alkyl aluminum compounds R 3 Al (R = Et, i -Bu, n -Bu, t -Bu and n -Hex); i -Bu 2 AlH; Et 2 AlCl and EtAlCl 2 in the hydrogenation of β-keto sulfones. The compounds i -Bu 2 AlH, i -Bu 3 Al and Et 3 Al are the at best reducing agents of β-keto sulfones to β-hydroxy sulfones. In reactions of β-keto sulfones with aluminum trialkyls, hydroalumination products with β-hydroxy sulfone ligands [R 2 AlOC(C 6 H 5 )CH 2 S(O) 2 ( p -R 1 C 6 H 4 ] n [where n = 1,2; 2aa : R = i -Bu, R 1 = CH 3 ; 2ab : R = i -Bu, R 1 = Cl; 2ba : R = Et, R 1 = CH 3 ; 2bb : R = Et, R 1 = Cl] and {[Et 2 AlOC(C 6 H 5 )CH 2 S(O) 2 ( p -ClC 6 H 4 ]∙Et 3 Al} n 3bb 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 β-hydroxy sulfones. Hydroalumination reaction of β-keto sulfones with alkyl aluminum compounds and subsequent hydrolysis of the complexes is a simple and very efficient method of β-hydroxy sulfones synthesis.