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Coordination of an electrophilic transition-metal fragment, ML n , to the carbocyclic ring of benzothiophene (BT) to form (η6-BT)ML n m + activates a C−S bond to cleavage by the weak nucleophile Pt(PPh3)3, with concomitant insertion of Pt(PPh3)2. The rate of formation of the resulting metallathiacyclic insertion products, {(η6-BT·Pt(PPh3)2}ML n m +, depends on the metal fragment in the order ML n = Ru(C6Me6)2+, Mn(CO)3 + > FeCp+, RuCp+ ≫ Cr(CO)3, with no reaction occurring in the absence of a ML n activating group. All of the unsubstituted benzothiophene complexes undergo regiospecific cleavage of the olefinic C−S bond rather than the aryl C−S bond, which is likely a consequence of steric congestion that would exist if insertion had occurred at the latter site. The X-ray structures of the metallathiacycles {(η6-BT·Pt(PPh3)2}Mn(CO)3 + and {(η6-BT·Pt(PPh3)2}FeCp+ are reported. The complexes (η5-2,5-dimethylthiophene)Mn(CO)3 + and (η6-dibenzothiophene)Mn(CO)3 + also undergo rapid C−S bond cleavage with metal insertion in the presence of Pt(PPh3)3. The results suggest that π-adsorption of a thiophenic substrate on a catalyst surface in hydrodesulfurization reactions is a viable way to facilitate C−S bond cleavage, as well as subsequent desulfurization and hydrogenolysis.

The reactions of [Fe2(cp)2(CO)2(μ-CO)(μ-CSMe)]CF3SO3 (1; cp = η-C5H5) with a variety of carbon nucleophiles result in CC bond formation at different sites of the molecule. (allyl)MgCl (allyl = C3H5) undergoes cp addition to form [Fe2(cp)(η4-C5H5-allyl)(CO)2(μ-CO)(μ-CSMe)] (2) and the alkylidene complex [Fe2(cp)(η-C5H4-allyl) (CO)2(μ-CO){μ-C(SMe)H}] (3), derived from cp to μ-C hydrogen migration. Li2Cu(CN)R2 adds at the μ-C atom to yield [Fe2(cp)2(CO)2(μ-CO){μ-C(SMe)R}] (R = Ph, 4; R = Me, 8), [FeFe(cp)2(CO)(μ-CO){μ-C(SMe)R}] (R = Ph, 5; R = Me, 9), and [Fe2(cp)2(CO)(μ-CO){μ-C(η2-Ph)Ph}] (6) or the vinylidene derivative [Fe2(cp)2(CO)(μ-CO)(μ-CCH2)] (10) in the case of phenyl or methyl organocuprate reagents, respectively. The latter complexes are the result of CSMe bond breaking occurring, through different reaction paths, in 4 and 8. Likewise, the formation of [Fe2(cp)2(CO)(μ-CO){μ-CC(CN)2}] (11) from 1 and NaCH(CN)2 occurs via a direct addition at the μ-C carbon followed by HSMe elimination. The nucleophilic attack at the terminal CO in 1 is achieved with LiC⋮CPh, which forms two new CC bonds in the alkylidene complex [FeFe(cp)2(CO)(μ-CO){μ-C(SMe)C(O)CCPh}] (12) after C(O)CCPh migration from Fe to the bridging carbene carbon. The analogous [FeFe(cp)2(CO)(μ-CO){μ-C(SMe)C(O)(2-th)}] (13; 2-th = 2-C4H3S) and [Fe2(cp)(η4-C5H5-(2-th)(CO)2(μ-CO)(μ-CSMe)] (14) are obtained from 1 and Lith via addition at the CO and cp groups, respectively. The relevance of these reactions is discussed in terms of selective CC bond formation that, if it occurs at the cp or CO terminal ligands, favors the hydrogen migration (e.g. formation of 3) or the carbyne−carbonyl migratory coupling (e.g. formation of 12 and 13), respectively. The X-ray structures of [Fe2(cp)2(CO)(μ-CO){μ-C(η2-Ph)Ph}] (6) and [FeFe(cp)2(CO)(μ-CO){μ-C(SMe)C(O)(2-th)}] (13) have revealed the peculiarity of the Ph and SMe group coordination to the iron. Their structural features are discussed in comparison with those of analogous complexes.

We have recently disclosed that trimethylsilyl trifluoromethanesulfonate (TMSOTf) promotes the formal [1,3]dipolar cycloaddition of allyltrimethylsilane1 and silyl enol ethers2 with aldonitrones 1. Reaction conditions are more mild than those required by the related thermal processes;3 in fact, cycloadditions take place at -20 to 20 °C in chlorinated solvents in the presence of a slight molar excess of TMSOTf. We have shown that TMSOTf converts a nitrone into a highly electrophilic IV-(silyloxy)iminium ion 2;4 the overall process involves nucleophilic addition of the silylated nucleophile5 to 2 to give the /3-silylated carbonium ion 3 followed by a fast ring closure to the isoxazolidine 4, as depicted in Scheme 1. Even though TMSOTf is regenerated in the cyclization step, it is tightly bound to isoxazolidine 4 and must be used in stoichiometric amount to get good conversions.As an extension of our previous work, here we report a synthesis of bicyclic isoxazolidines 6 starting from nitrones la-j and 2-[(trimethylsilyl)oxy]furan (5) (Scheme 2). 2-[(Trimethylsilyl)oxy]furan ( 5) has been recently recognized to act as a powerful reagent for straightforward syntheses of butenolides and for four-carbon elongation of aldoses;6 in these reactions 5 undergoes aldolization as well as alkylation exclusively at the C-5 position.7We found that 5 reacts with nitrones at -20 °C in dichloromethane in the presence of 5-35% of TMSOTf to give 2(5/f)-furanone 5-iV-hydroxymethanamines 8. In order to account for the reaction mechanism, we propose the catalytic cycle depicted in Scheme 3.Lactones 8 were detected, after hydrolysis with water, as the major components by IR (vCo at 1745 cm-1), 1H

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