Complex hydrides sulfur oxides

It was shown that the oxidation product obtained by treatment of bulbocapnine methyl ether (25f) with iodine in ethanol/water is not the tetradehydroaporphinium salt, as reported by Gadamer and Kuntze (443), but a dimer of the structure 37 (441, 441a) (Scheme 9). Reduction of this compound with zinc in dilute sulfuric acid gives racemic bulbocapnine methyl ether (25f), whereas reduction with complex hydrides affords the dimers 38 and 39. 

There are several methods reported in the literature for transforming vicinal diols into ct-diketones while avoiding the risk of C-C bond cleavage.26 Examples include the standard Swem conditions (dimethyl sulfoxide and oxalyl chloride followed by triethylamine), or the use of DMSO activated by acetic anhydride, pyridine-sulfur trioxide complex, or dicyclohexylcarbodiimide (Mq/J-att oxidation). Diones are also obtained by treatment with benzalacetone as a hydride acceptor in the presence of catalytic amounts of tris(triphenylphosphine)ruthenium dichlonde [(PPh RuCFl.27 Recent developments include the use of w-iodoxyben/.oic acid28 or the oxoammonium salt of 4-acctamidoletramethylpipcridine-1-oxyl and y -toluencNulfonic acid.29... 

Fio. 19. Proposed electron transfer pathways for oxidation and reduction of NADH/NAD and NADPH/NADP, and energy coupling site 1 in complex I. Where applicable broken arrows indicate energy-linked electron or hydride ion transfer. FeS, iron-sulfur center. 

Although thiol and hydride/thiolate complexes are known, there are few studies which show that the hydrogen can move between metal and sulfur [35-38]. The transfer of a proton from sulfur to metal has been proposed before. For example, the so-called oxidative-addition of RSH to [IrCl(CO)(PPh3)2] has been suggested to involve a three-centre, Ir-H-SR transition state in which the lengthening of the S-H bond is synchronous with the binding of these two atoms to the iridium centre [39]. More recently [40] an agostic Os—H-S interaction has... 

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