Dichloromethane reaction with selenides

Treatment of the selenides 165 with /ftt-butyl hypochlorite in a dichloromethane solution followed by reaction with triethylamine yielded the enantiomerically pure spiroselenuranes 166 (Equation 43) <1998TA3303>. 

Syntheses of Alkylidene cyclopropanes Via the Selenonium route The selenonium route proved to be more valuable. It has been specifically designed by us to replace the deficient selenoxide route (Scheme 38). It was expected to produce alkylidene cyclopropanes by a mechanism which mimics the selenoxide elimination step but which involves a selenonium ylide in which a carbanion has replaced the oxide. Cyclopropyl selenides are readily transformed to the corresponding selenonium salts on reaction with methyl fluorosulfonate or methyl iodide in the presence of silver tetrafluoroborate in dichloromethane at 20 °C and, as expected, methylseleno derivatives are more reactive than phenyl-seleno analogs. Alkylidene cyclopropanes are, in turn, smoothly prepared on reaction of the selenium salts at 20 °C with potassium tert-butoxide in THF (Scheme 38). Mainly alkyl cyclopropenes form at the beginning of the reaction. They then slowly rearranges, in the basic medium, to the more stable alkylidene cyclopropanes( 6 kcal/mol). In some cases the complete isomerisation requires treatment of the mixture formed in the above reaction with potassium fcrt-butoxide in THF. The reaction seems to occur via a selenonium ylide rather than via a P-elimina-tion reaction promoted by the direct attack of the /crt-butoxide anion on the P-hydrogen of the selenonium salt, since it has been shown in a separate experiment that the reaction does not occur when a diphenylselenonium salt (imable to produce the expected intermediate) is used instead of the phenyl-methyl or dimethyl selenonium analogs. It has also been found that the elimination reaction is the slow step in the process, since styrene oxide is formed if the reaction is performed in the presence of benzaldehyde which traps the ylide intermediately formed... 

Enantioselective conversions of aryl benzyl selenides to N-tosylselenimides 28 with [(tosylimino)iodo]benzene, cuprous triflate, and the chiral bis(oxazo-line) 22 have recently been demonstrated (Scheme 16) [37,38]. Because benzyl phenyl selenide undergoes uncatalyzed imidation with Phi = NTs in acetonitrile (46 % yield) or dichloromethane (trace yield), toluene was selected as the solvent for the asymmetric imidation reactions. Furthermore, in order to avoid racem-ization of 28 by moisture, molecular sieves were added to the reaction medium. 

The only derivative of Re3X9 that contains a selenium ligand is one of stoichiometry Re3Cl9L2-CH2Cl2 that is formed by the reaction of Re3Cl9 with 1,2,5-triphenylphosphole selenide in refluxing dichloromethane.186... 

The stereoselective formation of /3-hydroxy selenides has also been reported 36 in the reaction of alkenes with, V-(phenylseleno)phthalimide or the succinimide derivative in aqueous acetonitrile or dichloromethane. The use of phenylselenenyl chloride under these conditions gives similar results (Table 5)37. 

Oxidations with m-chloroperoxybenzoic acid are carried out in solutions in hexane, dichloromethane, chloroform, methanol, or tetrahydro-furan at temperatures ranging from -78 to 40 C. The applications of m-chloroperoxybenzoic acid are epoxidation [287, 314, 315, 316] the Baeyer-Villiger reaction [286, 315, 317, 378] and the oxidation of primary amines to nitro compounds [379], of tertiary amines to amine oxides [320], of sulfides to sulfoxides [327, 322, 323, 324], and of selenides to selenones [325]. Secondary alcohols are oxidized to ketones in the presence of hydrogen chloride [326], and acetals are oxidized to esters with boron trifluoride etherate as a catalyst [327]. The addition of potassium fluoride to reaction mixtures facilitates product isolation, because both m-chloroben-zoic acid and the unreacted m-chloroperoxybenzoic acid are precipitated... 

A soln. of bis[isopropyl(thiocarbonyl)] sulfide in hexane added to a soln. of freshly prepared Na-benzeneselenolate in 3 1 dichloromethane/methanol at 0°, and stirred for 30 min - Se-phenyl 2-propanecarboselenothioate. Y 77%. F.e., also from thiocar-boxylic acid chlorides (with selenolates or silyl selenides), and reactions s. S. Kato et al.. Bull. Chem. Soc. Japan 61, 3931-J2 (1988). 

Several chalcogenide catalyzed MBH-type reactions are reported [146], Instead of the common ferf-amines or phosphanes, also higher organochalcogenides can act as nucleophilic activator. Such Morita-Baylis-Hillman reactions catalyzed by sub-stoichiometric amounts of sulfides and selenides in the presence of Lewis acid to activate the carbonyl group were described by Kataoka and co-workers [147, 148]. The reaction of p-nitrobenzaldehyde and 2-cyclohexenone has been used for screening a series of chalcogenide catalysts in dichloromethane at room temperature. The best result was found when 10 mol% of chalcogenide where employed with a stoichiometric amount of TiCl in the presence of excess 2-cyclohexenone as Michael acceptor (3 equiv., Table 7.10). 

---