Allylic derivatives allyl halides

Lithiated indoles can be alkylated with primary or allylic halides and they react with aldehydes and ketones by addition to give hydroxyalkyl derivatives. Table 10.1 gives some examples of such reactions. Entry 13 is an example of a reaction with ethylene oxide which introduces a 2-(2-hydroxyethyl) substituent. Entries 14 and 15 illustrate cases of addition to aromatic ketones in which dehydration occurs during the course of the reaction. It is likely that this process occurs through intramolecular transfer of the phenylsulfonyl group. 

A fundamental problem in the alkylation of enamines, which is inherent in the bidentate system, is the competition between the desired carbon alkylation and attack at the nitrogen. With unactivated alkyl halides (3,267), this becomes especially serious with the enamines derived fromcycloheptan-one, cyclooctanone, cyclononanone, and enamines derived from aldehydes. Increasing amounts of carbon alkylation are found with the more reactive allyl and benzyl halides (268-273). However, with allyl halides one also observes increasing amounts of dialkylation of enamines. 

Halogen atoms can be stereoselectively introduced by ring-opening of y-azir-idinyl-a,P-enoates (Scheme 2.39). Treatment of 149 with diethylaminosulfur tri-fluoride (DAST) results in stereospecific ring-opening to yield fluorinated derivative 150 [59]. A related stereoselective conversion of y-aziridinyl-a,P-enoates 151 into allyl halides 152 by use of lithium halide in the presence of Amberlyst 15 was also reported recently [60]. 

In another method for the coupling of two different allylic groups, a carbanion derived from a P,y-unsaturated thioether couples with an allylic halide. The... 

Allyltitaniums from Allyl Halides or Allyl Alcohol Derivatives and Ti(ll) and their Synthetic Utility... 

Typical procedure for the preparation of allyltitanium derivatives from allyl halides via oxidative addition, and in situ reaction with aldehydes [57,59]... 

The reaction of methylenesulphones with allyl halides in the presence of quaternary ammonium salts produces the 1-allyl derivatives [52], unlike the corresponding reaction in the absence of the catalyst in which the SN- product is formed (Scheme 6.5). In contrast, alkylation of resonance stabilized anions derived from allyl sulphones produces complex mixtures [51] (Scheme 6.6). Encumbered allyl sulphones (e.g. 2-methylprop-2-enyl sulphones) tend to give the normal monoalkyl-ated products. Methylene groups, which are activated by two benzenesulphonyl substituents, are readily monoalkylated hydride reduction leads to the dithioacetal and subsequent hydrolysis affords the aldehyde [61]. 

Alkylation of P-dicarbonyl compounds and p-keto esters occurs preferentially on the carbon atom, whereas acylation produces the 0-acyl derivatives (see Chapter 3). There are indications that C- and 0-alkylated products are produced with simple haloalkanes and benzyl halides, but only C-alkylated derivatives are formed with propargyl and allyl halides [e.g. 90]. Di-C-alkylation frequently occurs and it has been reported that the use of tetra-alkylammonium 2-oxopyrrolidinyl salts are more effective catalysts (in place of aqueous sodium hydroxide and quaternary ammonium salt) for selective (-90%) mono-C-alkylation of p-dicarbonyl compounds [91]. 

With the ready availability of 2-fluoro-allylic halides and a-fluoroacrylic acid derivatives, incorporation of a pendant fluorovinyl unit is easier than ever. The utility of these products is markedly enhanced by the reactivity of the fluorovinyl unit in olefin metathesis reactions. Some success has been found in cyclization reactions as shown below [83] (Scheme 36). 

Scheme 57 illustrates an example of this process coupling of the lithio reagent derived from vinyl stannane 237 with epoxide 242 leads to the C-disaccharide derivative 243 in good yield. A double transmetallation to give an organocopper reagent 244 can facilitate the C-glycosylation reaction with allyl halides [80] (Scheme 58). 

Asymmetrically substituted allyl magnesium compounds often react to yield products derived from both the parent allyl halide and the corresponding aUylic isomer, in varying relative yields . Depending on the arrangement of the substituents, cis and trans... 

Fluorinated vinylzinc reagents readily react (particularly with Cu(I)X catalysis) with allyl halides at room temperature (equation 63)57. With a substituted allyl halide, the 2-propenyl reagent gave products of both a- and -attack. The predominant product is derived from attack at the less hindered position (equation 64)5. 

Certain allyl cations react quite efficiently with nonactivated alkenes to give cyclobutanes. Such cations can be generated by Lewis acid catalyzed dehalogenation of allyl halides, protonation of conjugated dienes and Lewis acid eomplexation of conjugated carbonyl derivatives. For example, 2-chloro-2,4-dimethylpent-3-ene ( ) reacts with alkenes in the presence of zinc(II) chloride to give the corresponding cyclobulanes.1 Alkyl substitution of the allyl cation at the 2-position results in [3 + 2]-cycloaddition products. 

Reaction of methyl iododifluoroacetate with copper in HMPA affords the carboalkoxydifluoromethylene copper reagent, which couples with aryl, alkenyl, alkyl, alkynyl and allyl halides to give the corresponding 2,2-difluoroester derivatives [261] (Scheme 87). 

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