6-cyano-2,2-dimethylchromene

Benzylidene derivatives of the enantiomers of 1,2-diaminocyclohexane are also excellent ligands for the Cu(I)-catalyzcd asymmetric aziridination of olefins with 64, but the enantioselectivities using acyclic alkenes were about the same as those using ligand (S, S )-6658. When (5, 5 )-bis-(2,4-dichlorobenzylidenediamino)cyclohexane [(S,S)-67] was employed with C.u(I) triflate, 6-cyano-2,2-dimethylchromene (68) was converted to (R,R) 69 in a 75% yield with an ee greater than 98%58. 

The group of Wang has prepared a series of Mn(salen) complexes containing a pyrrolidine backbone (49, Figure 9) 6-nitro- and 6-cyano-2,2-dimethylchromene are epoxidized in 86-99% yield and 86-96% ee <2006JCT248>. 

Kureshy [198] had also carried AE with a poly-salen. The poly-salen 316 derived from chiral diphenylethylenediamine (2 mol%) (Scheme 132) and NaOCl in the presence of cooxidant (NMO, 4-PPNO, PyNO, DMSO) forming the oxidative reagent were used for the epoxidation of styrene, indene and 6-cyano-2,2-dimethylchromene. In all cases, the best results in term of... 

Freire and coworkers described the intercalation of a chiral phosphonic acid derivatised [Mn (sa/e )Cl] complex within KlO-Montmorillonite layers by ion-exchange with the interlayer potassium cations. The catalytic performance of the heterogeneous catalyst (denoted as [Mn (sa/en)Cl] K10) was evaluated in the enantioselective epoxidation of styrene, a-methylstyrene and 6-cyano-2,2-dimethylchromene, at 0 °C in dichloromethane or acetonitrile, using three different oxidant systems m-CPBA/NMO, PhIO and NaOCl the results are summarised in Table 11.1. 

Another approach, keeping the C2 symmetry, consisted in the immobilization of the catalyst on a TentaGel amine resin via the pyrrolidine part of a pyrrolidine-salen instead of the aromatic rings (Scheme 130) [195]. In presence of NaOCl or w-CPBA, with 4 mol% of catalyst 313 all imderwent AE of 2,2-dimethylchromene, 6-cyano-2,2-dimethylchromene and 1-phenylcyclohex-l-ene in high yields, more than 70% and with enantioselectivities of 82%, 86% and 68% respectively. In these conditions, decomposition of this catalyst was observed. 

Kureshy and coauthors [82] also reported that chiral Mn(Salen) catalyst immobilized in the nanopores of MCM-41 and SBA-15 (Scheme 10.14) showed higher enantioselectivity (70% ee) than its homogeneous counterpart (45% ee) for the enantioselective epoxidation of styrene with aqueous NaOCl as the oxidant. In addition, the immobilized chiral Mn(Salen) could smoothly catalyze the epoxidation of bulkier alkenes such as 6-cyano-2,2-dimethylchromene into their epoxides with enanatioselectivity (up to 92% ee) comparable to those of the homogeneous counterparts. The heterogeneous catalyst could be recycled four times without notable loss of activity and enantioselectivity. 

---