Zinc iodide benzylic compounds

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]. 

A significant amount of work has been focused on the synthesis of benzylic and allylic phosphonates. Historically, popular synthetic routes entailed the conversion of the alcohol into a good leaving group such as a mesylate or a halide followed by conversion to the organophosphorus compound. A more efficient synthesis would entail the direct conversion of the alcohol into the phosphonate. To this end, Wiemer described the use of zinc iodide as a Lewis acid catalyst for the direct conversion of benzylic and allylic alcohols into phosphonates (Schemes 4.51 and 4.52) [104]. Zinc iodide is inexpensive and... 

Functionalized organozinc halides are best prepared by direct insertion of zinc dust into alkyl iodides. The insertion reaction is usually performed by addition of a concentrated solution (approx. 3 M) of the alkyl iodide in THF to a suspension of zinc dust activated with a few mol% of 1,2-dibromoethane and MeaSiCl [7]. Primary alkyl iodides react at 40 °C under these conditions, whereas secondary alkyl iodides undergo the zinc insertion process even at room temperature, while allylic bromides and benzylic bromides react under still milder conditions (0 °C to 10 °C). The amount of Wurtz homocoupling products is usually limited, but increases with increased electron density in benzylic or allylic moieties [45]. A range of poly-functional organozinc compounds, such as 69-72, can be prepared under these conditions (Scheme 2.23) [41]. 

A branched-chain iodo sugar derivative, l,5-anhydro-4,6-0-benzyl-idene-2,3-dideoxy-3-C-(iodomethyl)-D-rifoo-hex-l-enitol [4,6-O-ben-zylidene-3-deoxy-3-C-(iodomethyl)-D-allal] (200), is one of the products formed on treatment of methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-en/thro-hex-2-enopyranoside (77) with the Simmons-Smith reagent (diiodomethane and zinc-copper couple).123,212 Compound 200 displays high solvolytic reactivity, an observation that has been rationalized by supposing the formation of the highly stabilized carbonium ion213 (201). Thus, under conditions wherein methyl 2,3,4-tri-0-acetyl-6-deoxy-6-iodo-a-D-glucopyranoside required more than 24 hours to react appreciably with an excess of silver nitrate in 50% aqueous p-dioxane buffered with silver carbonate, the iodide 200 was hydrolyzed completely in less than 1 minute the product of hydrolysis of 200 is the cyclopropyl aldehyde 202. Methanolysis of... 

Arene(tricarbonyl)chromium complexes, 19 Nickel boride, 197 to trans-alkenes Chromium(II) sulfate, 84 of anhydrides to lactones Tetrachlorotris[bis(l,4-diphenyl-phosphine)butane]diruthenium, 288 of aromatic rings Palladium catalysts, 230 Raney nickel, 265 Sodium borohydride-1,3-Dicyano-benzene, 279 of aryl halides to arenes Palladium on carbon, 230 of benzyl ethers to alcohols Palladium catalysts, 230 of carboxylic acids to aldehydes Vilsmeier reagent, 341 of epoxides to alcohols Samarium(II) iodide, 270 Sodium hydride-Sodium /-amyloxide-Nickel(II) chloride, 281 Sodium hydride-Sodium /-amyloxide-Zinc chloride, 281 of esters to alcohols Sodium borohydride, 278 of imines and related compounds Arene(tricarbonyl)chromium complexes, 19... 

Palladium catalysed coupling reaction of a heteroaromatic zinc compound with a functionalized aryl iodide preparation of N-benzyl-6-(4-ethylcarboxyphenyi)-purine33... 

Direct Reaction of Zn with Alkyl Halides. The direct insertion see Insertion) reaction of Zn metal into alkyl halides - alkyl iodides being the ideal snbstrates - is a nseful reaction to prepare simple or polyfunctional organozinc halide compounds (equation 1). With primary alkyl iodides, the reaction requires an excess of Zn dnst (ca. 3 eqniv), previonsly treated with few mol % of 1,2-dibromoethane and TMSCl, and a temperature of 40 °C in THF. In these conditions, secondary alkyl iodides react at room temperatnre and benzylic and allylic bromides at 0 °C. The insertion see Insertion) into less activated C-X bonds may reqnire more reactive forms of zinc (Riecke zinc), higher temperatures, or the use of polar see Polar Compounds) solvent or cosolvent. 

In an early example of this reaction aryl and benzyl zinc halides were coupled with aryl halides (equation 40) (102). Alkynyl zinc compounds cross-couple with aryl halides (iodides or bromides) in the presence of a Pd catalyst (equation 41) (103) or alkynyl iodides can be coupled with aryl and alkenyl zinc compounds (equation 42) (100). 

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