Halides, acyl from alkenes

The acylpalladium complex formed from acyl halides undergoes intramolecular alkene insertion. 2,5-Hexadienoyl chloride (894) is converted into phenol in its attempted Rosenmund reduction[759]. The reaction is explained by the oxidative addition, intramolecular alkene insertion to generate 895, and / -elimination. Chloroformate will be a useful compound for the preparation of a, /3-unsaturated esters if its oxidative addition and alkene insertion are possible. An intramolecular version is known, namely homoallylic chloroformates are converted into a-methylene-7-butyrolactones in moderate yields[760]. As another example, the homoallylic chloroformamide 896 is converted into the q-methylene- -butyrolactams 897 and 898[761]. An intermolecular version of alkene insertion into acyl chlorides is known only with bridgehead acid chlorides. Adamantanecarbonyl chloride (899) reacts with acrylonitrile to give the unsaturated ketone 900[762],... 

The reaction between a phosphonium ylidc derived from a fluorotrihalomcthane and an acetyl halide leads to the ylide acylation product 9 and the salt 10 by the Wittig reaction. This has been used to obtain alkenes 11 from acyl halides. ... 

This reaction was first reported by Nenitzescu in 1931. It is the formation of an a,p-unsaturated ketone directly by aluminum chloride-promoted acylation of alkenes with acyl halides. Therefore, it is known as the Darzens-Nenitzescu reaction (or Nenitzescu reductive acylation), or Nenitzescu acylation. Under such reaction conditions, Nenitzescu prepared 2-butenyl methyl ketone from acetyl chloride and 1-butene and dimethylacetylcyclohex-ene from acetyl chloride and cyclooctene. However, in the presence of benzene or hexane, the saturated ketones are often resolved, as supported by the preparation of 4-phenyl cyclohexyl methyl ketone from the reaction of cyclohexene and acetyl chloride in benzene, and the synthesis of 3- or 4-methylcyclohexyl methyl ketone by refluxing the mixture of cycloheptene and acetyl chloride in cyclohexane or isopentane. This is probably caused by the intermolecular hydrogen transfer from the solvent. In addition, owing to its intrinsic strain, cyclopropyl group reacts in a manner similar to an oleflnic functionality so that it can be readily acylated. It should be pointed out that under various reaction conditions, the Darzens-Nenitzescu reaction is often complicated by the formation of -halo ketones, 3,)/-enones, or /3-acyloxy ketones. This complication can be overcome by an aluminum chloride-promoted acylation with vinyl mercuric chloride, resulting in a high purity of stereochemistry. ... 

As with carboxylic acids obtained by palladium hydroxycarbonylation, their derivatives esters, amides, anhydrides and acyl halides are synthesized from alkenes, CO and HX (X = OR, NR2 etc.). The Pd-catalyzed methoxycarbonylation is one of the most studied reactions among this type of catalyzed carbonylations and has been reviewed and included in reports of homogeneous catalysis.625, 26 The methoxycarbonylation has been applied to many different substrates to obtain intermediates in organic syntheses as well as specific products. For instance, the reaction has been applied for methoxycarbonylation of alkynes666 Highly efficient homogeneous Pd cationic catalysts have been reported and the methoxycarbonylation of alkynes has been used to develop economically attractive and environmentally benign process for the production of methyl... 

Cyclopentadienes can be prepared by double Michael addition of zirconacyclopentadienes with propynoates <1997CC2069> or nucleophilic attack of zirconacyclopentadienes on acyl halides mediated by copper(l) chloride and accompanied by elimination <1995CC1503, 1996TL7521>. Tetraethylzirconacyclopentadiene with benzal chloride in THF in the presence of copper(l) chloride and DMPU yield l,2,3,4-tetraethyl-5-phenylcyclopenta-l,3-diene <2000TL7471>. A series of other similar compounds were prepared from tetra- -propylzirconacyclopenta-diene and 0 ,Q -dichlorotoluene, tetra- -butylzirconacyclopentadiene and 0 ,Q -dichlorotoluene or 0 ,Q -dibromotoluene, as well as some other combinations. Tetraethylzirconacyclopentadiene reacts with l,l-dibromo-l-alkene-3-ynes under the same conditions (copper(l) chloride and DMPU) to yield alkynylfulvenes. 

Alkenes were reacted with thallium triacetate and azidotrimethylsilane to give 0-azidoalkyl thallium compounds, which were converted in situ to aziridinylazothallium compounds70,71. Only in the case of norbornene derivatives were the initial adducts (cxo.cw-azido-thallium compounds) isolated72. The aziridinylazothallium compound derived from cyclohexene 1 underwent thermal decomposition to give the trans-1,2-diazide, 2 in low yield. However, on treatment with acyl halides or trifluoroacetic anhydride, compound 1 afforded the corresponding 0-halo or 0-trifluoroacetoxy azides70. 

Friedel-Crafts acylation of alkenes (Daizens-Nenitzescu reaction ) with unsaturated acylium ions generated from acid halides and Lewis acids constitutes a general synthesis of divinyl ketones. 

Pd is very widely used in organic synthesis27 and we shall meet r 2 alkene and r 3 allyl complexes later. This chapter will end with a brief description of Pd o-complexes. Stable Pd o-complexes can be formed from ArX, MeX, and a few blocked alkyl compounds with no P-hydrogens. They react well with alkyl and acyl halides, but a major application is in carbonylation reactions.28... 

With anhydrides, aluminum chloride reacts to form the acid chloride complex. Zinc chloride is more commonly used with acid anhydrides, although this is restricted practically to acetic and other simple anhydrides that can be used as the reaction solvent. This nevertheless remains a useful reagent for acylations, giving predominantly nonconjugated products. Active zinc compounds prepared from a zinc-copper couple and alkyl halides also promote the acylation of alkenes by acyl chlorides at room temperature. ... 

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