Highly stereoselective epoxidation of (-)-alpha-pinene over chiral transition metal (salen) complexes occluded in zeolitic hosts

Various transition metal complexes of seven different salen ligands have be en incorporated in specially modified zeolitic host materials. The thus imm obilized sterically demanding complexes have been tested in the diastercose lective epoxidation of (-)-alpha -pinene in the liquid phase in an autoclav e at room temperature and elevated pressure using O-2 as oxidant. In most c ases conversions of 100% could be achieved. Best results so far-100% conver sion, 96% epoxide chemoselectivity and 91% diastereomeric excess-have been obtained in the presence of the entrapped [(R,R)-(N,N')-bis(3,5-di-tert-but ylsalicylidene)-1,2-diphenylethylenediamino]cobalt(II) = Co(salen-5) comple x. Computer simulations were done in order to prove that the reaction can t ake place inside the pore system, i.e., (-)-alpha -pinene is able to diffus e through the microporous entrances of the carrier material.