Rhodium chloride allylic oxidation

Subsequently to rhodium coordination with the enyne to form X, oxidative addition with the allyl chloride affords a rhodium-7r-allyl complex. Then isomerization... 

The isomerization of allyl ethers to 1-propenyl ethers, which is usually performed with potassium tert-butoxide in dimethyl sulfoxide, can also be carried out under milder conditions using tris(triphen-ylphosphine)rhodium chloride,208 and by an ene reaction with diethyl azodicarboxylate,209,210 which affords a vinyl ether adduct. Removal of an O-allyl group may be achieved by oxidation with selenium dioxide in acetic acid,211 and by treatment with N-bromosuccinimide, followed by an aqueous base.201,212... 

A combination of rtiodium(III) chloride with silver acetate, and treatment of rhodium(II) acetate in acetic acid solution with ozone, are two methods for generation of the (is-oxotrimetal-acetato complex of rhodium [Rhs0(0Ac)6 2O)3]0Ac. This RhsO complex was found to effect catalytic allylic oxidation of alkenes efficiently to give the corresponding a -unsaturated carbonyl compounds in the presence of a reoxidant such as r-butyl hydroperoxide, although in disappointing yield (equation 44). 

The avermectins also possess a number of allylic positions that are susceptible to oxidative modification. In particular the 8a-methylene group, which is both allylic and alpha to an ether oxygen, is susceptible to radical oxidation. The primary product is the 8a-hydroperoxide, which has been isolated occasionally as an impurity of an avermectin B1 reaction (such as the catalytic hydrogenation of avermectin B with Wilkinson s rhodium chloride-triphenylphosphine catalyst to obtain ivermectin). An 8a-hydroxy derivative can also be detected occasionally as a metabolite (42) or as an impurity arising presumably by air oxidation. An 8a-oxo-derivative can be obtained by oxidizing 5-O-protected avermectins with pyridinium dichromate (43). This also can arise by treating the 8a-hydroperoxide with base. 

Isomerisation of allyl ethers to enol ethers by Wilkinson s catalyst in refluxing aqueous ethanol is accompanied by competing reduction of the double bond to the propyl ether409-412 However, treatment of Wilkinson s catalyst with butyl-lithium results in a red rhodium catalyst that is able to isomerise a wide range of substituted and unsubstituted allylic ethers without competing reduction.413-414 In the example shown in Scheme 4.215, the unpurified enol ether product was cleaved by treatment with a mixture of mercury(Il) chloride and mercury(II) oxide in acetone to liberate the anomeric centre in 91% yield for the two steps.413-414... 

Cuprous chloride tends to form water-soluble complexes with lower olefins and acts as an IPTC catalyst, e.g., in the two-phase hydrolysis of alkyl chlorides to alcohols with sodium carboxylate solution [10,151] and in the Prins reactions between 1-alkenes and aqueous formaldehyde in the presence of HCl to form 1,3-glycols [10]. Similarly, water-soluble rhodium-based catalysts (4-diphenylphosphinobenzoic acid and tri-Cs-io-alkylmethylam-monium chlorides) were used as IPTC catalysts for the hydroformylation of hexene, dodecene, and hexadecene to produce aldehydes for the fine chemicals market [152]. Palladium diphenyl(potassium sulfonatobenzyl)phosphine and its oxide complexes catalyzed the IPTC dehalogenation reactions of allyl and benzyl halides [153]. Allylic substrates such as cinnamyl ethyl carbonate and nucleophiles such as ethyl acetoactate and acetyl acetone catalyzed by a water-soluble bis(dibenzylideneacetone)palladium or palladium complex of sulfonated triphenylphosphine gave regio- and stereo-specific alkylation products in quantitative yields [154]. Ito et al. used a self-assembled nanocage as an IPTC catalyst for the Wacker oxidation of styrene catalyzed by (en)Pd(N03) [155]. 

Tin.—Allyltin compounds, especially under rhodium-complex catalysis, react with acyl chlorides to give allyl ketones or with aryl halides to give allylarenes. Bridgehead alkyl bromides are reduced on photolysis with Bu"3SnH, whilst the system (Bu"3Sn)20-Br2 oxidizes sulphides to sulphoxides. )V-(Alkoxycar-bonyl)amino-acids are obtained upon treatment of cyclic anhydrides with Bu3SnN3 and heating in an alcohol. ... 

An attractive pathway with a lot of potential uses the transition metal mediated reaction of organic halides with carbon monoxide. Suitable substrates are organic halides capable of oxidative addition to low-valent transition metal compounds. Insertion of carbon monoxide and reductive elimination of an acid halide will complete the catalytic cycle. In tins way it was shown tiiat allyl chloride yields butenoic acid chloride in >80% yield accor g to equation 22)P As well as palladium, rhodium and iridium also act catalytically. It is of no surprise that allylic halides, benzylic halides and aryl halides in particular are readily converted to acid halides. Simple aliphatic halid undergo the oxidative addition step more slowly and, if they cany hydrogen atoms on an sf hybridized C atom in the -position to the halogen atom, may give alkenes via 3-hydrogen elimination. Alkenes can also be converted to acid halides widi carbon monoxide in the presence of transition metal catalysts in solvents such as methylene chloride or tetrachloromethane. ... 

Palladium is a useful catalyst in several reactions which lead to keto-esters. p-Keto-esters react with allylic carbonates, with catalysis by palladium, in a decarboxylative allylation reaction. y-Keto-esters are prepared, in reasonable yield, by the palladium-catalysed regioselective oxidation of Py-unsaturated esters. y-Keto-esters are obtained in good yield by the palladium-catalysed Reformatsky reaction of ethyl bromoacetate and acid chlorides. Derivatives of y-ketopimelic acid are formed by the rhodium-carbonyl-catalysed reaction of derivatives of acrylic acid with carbon monoxide. A mild method for the conversion of propiolic esters into P-keto-esters via thiol addition has been reported (Scheme 63) it has been used in a formal synthesis of ( )-thienamycin. 

Ring expansion with Tamura et al. s Beckmann reagent, followed by dechlorination with Zn-Cu couple in methanol saturated with ammonium chloride, provided key pyrrolidinone intermediate 197 in 72% overall yield from 193. The intermediate 197 was then converted by using selenium dioxide and tcrt-butyl hydroperoxide into allylic alcohol (62%), which yielded the desired 1,3-diol 198 through rhodium-catalyzed hydroboration and oxidation as a 1 1 mixture of diastereomers in 72% yield. A seven-step reaction sequence then converted the diol 198 into (-l-)-retronecine 199, which was indistinguishable from an authentic sample of the natural product obtained by hydrolysis of natural monocrotaline (Scheme 16.29). ... 

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