1-Alkynyl Grignard reagents react with (SS)-(−)-menthyl p-toluenesulfinate in toluene to give optically active 1-alkynylp-tolylsulfoxides in high yields. The 1-alkynylsulfoxides thus obtained undergo a stereoselective hydroalumination followed by hydrolysis to afford the corresponding (E)-1-alkenylp-tolylsulfoxides with high optical purity.
The palladium catalyzed [3+2] cycloaddition of trimethylenemethane with a variety of vinylsulfoxides led to cycloadducts in good to excellent chemical yields and with a good level of asymmetricinduction.
On treatment with pyridine–camphorsulphonic acid, (S)-E-α-p-tolysulphinyl-α-β-enoates (4) undergo enantio-selectively a sequential prototropic shift and allylic sulphoxide–sulphenate rearrangement to produce (R)-E-γ-hydroxy-α,β-enoates (2) in 64–72% optical purity.
The cycloaddition of (Z) and (E)-vinyl sulfoxides with cyclic nitrones 1 and 2 is reported. Best diastereoselection is achieved with (Z)-vinyl sulfoxides 7a-d as dipolarophiles. This methodology allows the highly stereoselective synthesis of (+)-sedridine 9a, (-)-hygroline 10 and (-)-(2S)-N-carbomethoxypelletierine 11a. (C) 1997, Elsevier Science Ltd. All rights reserved.