Methylaluminium bis(4-substituted-2,6-di-tert-butylphenoxide): MAD and MABR Lewis acids

Abstract

(A) In the presence of the MAD Lewis acid, which complexes to the oxygen atom of the sulfoxide group, the radical cyclization/β-elimination tandem reaction leads to the R enantiomer 4. Without the MAD reagent, the S enantiomer is isolated (93% yield, > 96% ee). (B) A general method of six-membered carbocycles has been demonstrated, which involves the stereo-controlled cyclization of olefinic epoxides with MABR via the epoxide rearrangement and subsequent intramolecular ene reaction with high stereoselectivity. Treatment of 5 with MABR afforded trans-decalin-1-ol 6 as a sole isolable product with rigorous stereochemistry in 70% yield. (C) The MAD 1 or MABR 2 can be successfully utilised as a highly efficient nonchelating Lewis acid for achieving high stereoselectivity in 1,n asymmetric induction in cyclic as well as acyclic systems. Thus, Diels-Alder reaction of the acrylate of d-pantolactone and cyclopentadiene exhibits high diastereoselectivity not observable with ordinary Lewis acids.