Allylation Allyl bromides, reactions with

It is to be noted that besides allyl bromide, reactions with 3-methylallyl bromide are mentioned in this patent. What was unknown to Knorr at that time is that the products from the organometallic reagent of this halide result from the following allylic rearrangement (see Sect. 2.3.5) ... 

Allylic bromides reacted with KSCN/Si02 and BnNH30Ac/Al203 in one-pot gives the corresponding thioureas. Reactions of crotyl bromide with a series of alkylammonium acetates, with the exception of tert-butylammonium acetate, results in the corresponding thioureas (Scheme 49).130... 

Allylation of aldehydes. Aldehydes undergo selective allylation on reaction with allylic bromides and tin (1.2 equiv.) in H20/THF (5 1) in a sonicator.1 Similar results can be obtained with zinc powder in saturated aqueous NH4C1-THF (5 1).2 Example ... 

Allylation of organic halides. T wo laboratories2 have reported briefly that in the presence of a radical initiator organic halides undergo allylic substitution reactions with allyltrialkyltin compounds in moderate yield. This reaction was used in a recent Synthesis of the neurotoxin (+ )-perhydrohistrionicotoxin (7) to introduce the n-butyl tide chain.3 AI BN-catalyzed reaction of the bromide 2 with 1 proceeds in unexpectedly igh yield and with complete stereocontrol to give a single product 3. It is the tndesired isomer, but the desired stereochemistry is obtained by epimerization of the Intermediate ketone 5. The hydroxy lactam (6) had previously been used for the Synthesis of 7. 

Allylic halides and tosylates show enhanced reactivity toward nucleophilic displacement reactions by the Sn2 mechanism. For example, allyl bromide reacts with nucleophiles by the SN2 mechanism about 40 times faster than n-propyl bromide. 

Recently, Shiraishi and Goda [161 studied allylation of wood meal with allyl chloride or allyl bromide [Reaction (3)]. 

Diastereoselective macrocycUzation. A ke> step in a synthesis of the 14-membered cembranoid asperdiol (4) involves intramolecular ( yclization of the aldehydo allylic bromide (1) with chromium(II) chloride. The intermolccular version of this reaction is known to be anf/-selective (8,112). Treatment of racemic 1 with CrCl, (5 equiv., THF) results in a 4 1 mixture of the two anti-diastereomers 2 and 3 in 64% combined yield. The stereochemistry of this cyclization is evidently controlled by the remote epoxide group. The natural product was obtained by deprotection of 2 (Na/NH, 51% yield). 

Reaction of K-allylmckel bromide complexes with guinones. Allylic bromides react with nickel carbonyl to afford ir-allylnickel bromide complexes formulated as (1) in the case of ally bromide itself (2, 291 3, 210). Hegedus el al. have studied the reaction of... 

Another important metal for Barbier-type reaction is samarium. Allyl bromide reacts with a ketone and Sm to give the homoallylic alcohol. Samarium compounds, such as Sml2, can also be used with allylic halides. 

Various methods for the synthesis of allylamines have been reported.Reaction of allylic bromide (11) with amines gave Sn2 and Sn2 substitution products in the ratio Sn2 Sn2 ranging from ca. 1 20 for the reaction with piperidine to 9 1 for the reaction with diisopropylamine (Scheme 8). The product distribution changes with a slight change in the electron-withdrawing capacity of the arenesulfonyl group, as well as the structure of the amines. 

The synthesis of barbiturate 36 (see Scheme 4.7) was performed next. The sodium enolate of diethyl malonate was reacted with 43, providing 44, which was converted to 2,2-disubstituted malonate 45 by reaction with allyl bromide. Reaction of 45 with urea in the presence of t-BuOK as base afforded the barbiturate 46, which was submitted to oxidative one-carbon demolition by the action of KMn04 to give carboxylic acid 47. Compound 47 was esterified with ethanol to give the target 36, but unfortunately in modest yields. 

The zinc-promoted reaction of allylic bromides 262 with chiral TV-protected a-amino aldehydes 261 affords the anti diastereomer 263 with generally high selectivity (Table 10-29) [168]. The choice of protecting group is critical to the stereochemical outcome of the reaction. When the amino acids are protected by an N-Boc group, poor diastereoselectivity is observed. 

Chiral allylic indium reagents and achiral aldehydes. Chiral indium reagents have been generated by the oxidative metallation of allylic bromides, which bear remote stereogenic subunits. For example, the 1,4-asymmetric induction in the indium-mediated coupling of allyl bromides 298 with benzaldehyde affords the syn-adducts as the major products (Table 10-35) [199]. The stereoselectivity of the reaction improves with more sterically encumbered allyl bromides. 

Etherification of hindered tribromophenol with allyl bromide Reaction of sodium sulfide with benzyl chloride Reaction of amino acids and methanesulfonyl chloride Dichlorovinylation of carbazole in solid-liquid system... 

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