Dehalogenation under carbonylation conditions

This catalytic cycle, generating acetyl iodide from methyl iodide, has been demonstrated by carbonylation of anhydrous methyl iodide at 80°C and CO partial pressure of 3 atm using [(C6H5)4As][Rh(CO)2X2] as catalysts. After several hours reaction, acetyl iodide can be identified by NMR and infrared techniques. However, under anhydrous conditions some catalyst deactivation occurs, apparently by halogen abstraction from the acetyl iodide, giving rhodium species such as frans-[Rh(CO)2I4] and [Rh(CO)I4] . Such dehalogenation reactions are common with d8 and d10 species, particularly in reactions with species containing weak... 

Indium metal in water reduces a-halocarbonyl compounds and benzyl iodides to the corresponding dehalogenated products in excellent yields under sonication, though simple alkyl and aryl iodides remain inert under these conditions (Equation (97)).379 Similar dehalogenation in micellar systems in the presence of a catalytic amount of sodium dodecyl sulfate in water affords the corresponding parent carbonyl compounds in excellent yields (Equation (98)).380 The allylic iodide or acetate is reduced by indium into the corresponding 3-methylcephems and 3-methylenecephams in an aqueous system. The latter are converted into the former quantitatively under basic conditions (Scheme 110).381... 

A classical method using Na- or Li-liquid ammonia (Birch reduction conditions) is effective for reductive dehalogenations of aryl and vinylic halides, but it is not always successfully applied to alkyl halides, although cyclopropyl halides and bridgehead halogens are exceptions.Under such conditions, the reactions are often accompanied by side reactions, such as elimination, the Wurtz coupling reaction, cyclization and reduction of carbonyl compounds. An example, a synthesis of pentaprismane (1), is shown in Scheme 4. ... 

These reactions are usually heterogeneous, hence no meaningful data on their mechanisms have yet been obtained. It appears, however, that the reactions illustrated in Fig. 2 which occur under reducing conditions and where the metal carbonyls function as dehalogenating agents, probably go by paths as outlined in Fig. 3. In this scheme two main steps are envisioned,... 

Recently, Yamamoto et al. presented a new route to PPP using the zero-valent nickel complex itself (Scheme 6.15) as a dehalogenation reagent [59]. This reaction proceeds under mild conditions and can be applied to a wide range of aromatic compounds including those with carbonyl and cyano groups. 

The key butenolide needed by Buszek, for his synthesis of (—)-octalactin A, had already been prepared by Godefroi and Chittenden and coworkers some years earlier (Scheme 13.4).9 Their pathway to 10 provides it in excellent overall yield, in three straightforward steps from l-ascorbic acid. The first step entails stereospecific hydrogenation of the double bond to obtain L-gulono-1,4-lactone 13. Reduction occurs exclusively from the sterically less-encumbered ot face of the alkene in this reaction. Tetraol 13 was then converted to the 2,6-dibromide 14 with HBr and acetic anhydride in acetic acid. Selective dehalogenation of 14 with sodium bisulfite finally procured 10. It is likely that the electron-withdrawing effect of the carbonyl in 14 preferentially weakens the adjacent C—Br bond, making this halide more susceptible to reductive elimination under these reaction conditions. 

Alkylidynetricobalt nonacarbonyl complexes are an interesting class of clusters (78). They can be synthesized by treatment of a tri- or tetrahaloal-kane with cobalt carbonyl under phase-transfer conditions [e.g., 71] (28). Partially or completely dehalogenated by-products were often isolated from these reactions. 

Dehalogenation of a-hromo ketones. Treatment of ot-halo ketones with 1 equiv. of Co2(CO)a under phase-transfer conditions yields the dehalogenated ketone in high yield and traces of the 1,4-diketone. Yields of the methyl ketone are somewhat lower when the metal carbonyl is used in catalytic amounts. ... 

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