Zinc iodide carbonyl compounds

Cyclic Peroxides. CycHc diperoxides (4) and triperoxides (5) are soHds and the low molecular weight compounds are shock-sensitive and explosive (151). The melting points of some characteristic compounds of this type are given in Table 5. They can be reduced to carbonyl compounds and alcohols with zinc and alkaH, zinc and acetic acid, aluminum amalgam, Grignard reagents, and warm acidified iodides (44,122). They are more difficult to analyze by titration with acidified iodides than the acycHc peroxides and have been sucessfuUy analyzed by gas chromatography (112). 

Scheme 6.33 illustrates an example of some zinc-induced three-component coupling reactions of alkyl iodides, electron-deficient alkenes, and carbonyl compounds [51]. In this instance, the isopropyl radical is generated by a one-electron reduction of isopropyl iodide followed by elimination of iodide ion. The resulting radical then adds to acrylonitrile to form an a-cyano alkyl radical, which is con-... 

Alternatively, the silacyclopropane could be functionalized in situ through the addition of 30 mol% of zinc bromide (or zinc iodide) and a carbonyl compound to the reaction mixture, which produced oxasilacyclopentane 70 (Scheme 7.12).11,74... 

The zinc-mediated Reformatsky reaction is one of the classical methods for carbon-carbon bond formation. To date, various main group metals and transition metals have been used for this reaction. Rieke s activated indium powder mediates readily the coupling of ethyl a-bromoacetate and a variety of carbonyl compounds yielding /3-hydroxy esters in good yields (Scheme 87).3 Later, commercially available indium powder has been found to be equally effective for the indium-based Reformatsky reaction in THF.28 This indium Reformatsky reaction is accelerated by ultrasound irradiation (Scheme 88).322,323 Indium(i) iodide also mediates the Reformatsky reaction of aldehydes and ketones to give /3-hydroxy esters, presumably via organoindium(m) diiodide (Scheme 89).27... 

In the case of the allenyl copper intermediate 724, its alkylation with (iodomethyl)zinc iodide and carbonyl compounds afforded dienes 7251032 (Scheme 189). 

Due to silicon s higher affinity toward oxygen than carbon, the silyl iodide does not add directly across the vinyl ether double bond, but first reacts with the carbonyl compound to form a silyloxyalkyl iodide (25). In the presence of zinc iodide or iodine, this adduct adds to a vinyl ether, and the resulting vinyl ether-iodide adduct (26) initiates Znl2-mediated propagation (via 27). 

The cyclizations of 85 to 86 and of 87 to 88 represent the simple cases in which the internal nucleophile is the OH group of an alcohol [64,65]. An in situ generated hydroxy group, as in the addition of alcohols to carbonyl compounds, can also participate in phenylseleno-etherification reactions. This is examplified by the conversion of 89 into 90 in the presence of benzyl alcohol [66]. Another type of OH, which gives rise to these reactions is the enolic OH of /1-dicarbonyl compounds. Thus, Ley reported that compounds like 91 and 93 can be transformed into the cyclic derivatives 92 and 94 by treatment with N-PSP 11 in the presence of zinc iodide [67]. The cyclization of 95 to 96 represents a simple example of the selenolactonization process [68, 69]. It is interesting to note that the various cyclization reactions indicated in Scheme 14, which require different electrophilic selenenylating agents, can all be effected with phenyselenyl sulfate [70]. 

Allylation of carbonyl compounds. The reaction of allyl bromide with carbonyl compounds in the presence of zinc iodide is mediated by germanium(II) iodide. Ketones are less reactive than aldehydes and require an excess of the reagent and longer reaction times. 

The reaction of phosphorus ylides with carbonyl compounds as a route to fluoro-olefins is prone to complications (see Vol. 2, p. 46), but excellent yields of olefins are obtained upon dehalogenation of fluoroiodomethyltriphenylphos-phonium iodide with zinc-copper couple, e.g, ... 

Addition to Double Bonds in Zn-Barbier Reaction. Acetonitrile was used as the solvent in a surprising type of Zn-Barbier reaction, in which an alkyl iodide was reacted with (unactivated) zinc in the presence of both an activated olefin and a carbonyl compound [95]. 

Certain other reagents like samarium iodide in aqueous THF ", sodium dithionite in aqueous DMF , sodium sulfide in presence of polyethylene glycol " and metallic zinc along with nickel chloride. " Using the latter reagent (Zn/NiClj), a,P-unsaturated carbonyl compounds can be very readily reduced under ultrasound conditions (Scheme 105). 

Petrier and Luche have reported preliminary results from a study of the reductive properties of an aqueous Zn—NiCl2 (9 1) system [235]. Selective reduction of a,p-unsaturated carbonyl compounds was reported to occur in water/ethanol mixtures. Ultrasound increases the rate of the reaction, but its role is not simply that of an initiator as chemical activation of the zinc, using copper iodide or ammonium chloride, fails to effect reduction of the substrate. In addition, the authors stress that reaction does not occur in the absence of water. Reduction occurs preferentially at the double bond of the enone and is virtually complete before reduction of the carbonyl group begins. This degree of selectivity is not observed in the case of a,p-unsaturated aldehydes. 

Nakama and coworkers have shown that in the presence of a combination of BF3 OEt2 and zinc (11) iodide catalyst system, aldoximes react with a,P-unsaturated carbonyl compounds at ambient temperature, affording N-alkylated nitrones (114) in excellent yields (Equation 69) [72]. 

The metal compounds found by BP to enhance the activity of an iridium catalyst fall into two categories (i) carbonyl or halocarbonyl complexes of tungsten [117,119], rhenium [118,119], ruthenium [116,117,119], and osmium [116,117,119] (ii) simple iodides of zinc, cadmium, mercury,... 

The radical carbonylation of an alkyl iodide in the presence of Kim s sulfonyl oxime ethers [58, 59, 60] provides a new type of multicomponent coupling reaction where plural radical Cl synthons are consecutively combined [61]. In the transformation, allyltin was used to serve as a trap of benzenesulfonyl radical which converts sulfonyl radical to a tin radical, thus creating a chain. Scheme 14 illustrates such an example, where the product was easily dehydroxylated to give the corresponding tricarbonyl compound on treatment with zinc/AcOH. The radical acylation reaction by Kim s sulfonyl oxime ethers can be conducted under irradiation with the addition of hexamethylditin. This is an alternative path for achieving a similar transformation without the use of photolysis equipment. Scheme 15 illustrates several examples where carbon monoxide and Kim s sulfonyl oxime ethers are successfully combined to create new tandem radical reaction sequences [61],... 

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