Aldehydes allyl bromides

Functional group (FG) = Br, CONR2, CN, C02Et, C02tBu E-Y = aldehyde, allyl bromide... 

The reaction involves stirring aldehyde, allyl bromide, and stannous chloride in water and applying an electrolytic potential of 2.0 V with graphite electrodes. The cathode rednces Sn(ll or IV) salts to tin metal, which react with allyl bromide to generate allyltin(ll) bromide and diallyltin dibromide. These organotin species then allylate the aldehyde and the resulting homoallyl alcohol is extracted with diethyl... 

Functionalized boronic esters can be alternatively prepared from readily available iodoaryl boronic esters such as 17 and 18.1/Mg-exchange with i-PrMgCl- LiCl provides a bimetallic B/Mg-species such as 19 and 20 that react with a range of electrophiles (aldehyde, allyl bromide, acid chloride, 3-iodo-2[Pg.48]

The dianions derived from furan- and thiophene-carboxylic acids by deprotonation with LDA have been reacted with various electrophiles (Scheme 64). The oxygen dianions reacted efficiently with aldehydes and ketones but not so efficiently with alkyl halides or epoxides. The sulfur dianions reacted with allyl bromide, a reaction which failed in the case of the dianions derived from furancarboxylic acids, and are therefore judged to be the softer nucleophiles (81JCS(Pl)1125,80TL505l). 

Allyl bromide, Sb(OEt)3, 80°, 2-6 h, 85-98% yield. This method is chemoselective for aldehydes in the presence of ketones. 

Preparation of the aldehyde required for the synthesis of cyclothiazide (182) starts by carbonation of the Grignard reagent obtained from the Diels-Alder adduct (186) from allyl bromide and cyclopentadiene.The resulting acid (187) is then converted to the aldehyde (189) by reduction of the corresponding diethyl amide (188) with a metal hydride. 

In the preparation of the thiazides containing more highly functionalized side chains (183-185), an acetal of the aldehyde is usually used rather than the free carbonyl compound. Thus, trichlomethiazide (183) is prepared by reaction of 160 with the dimethyl acetal from dichloroacetaldehyde. In a similar vein, alkylation of the acetalthiol, 190, with allyl bromide affords 191. This yields altizide (184) on condensation with 160. Alkylation of 190 with 2,2,2-trifluoroethyl iodide gives 192. This leads to epithiazide (185) on condensation with 160. 

Treatment of allyl bromides with the complex obtained from tin(II) chloride and the disodium salt of diethyl 2,3-dihydroxybutanedioate gives an intermediate which reacts with aldehydes to provide homoallylic alcohols with 50-65% ee. Lower enantiomeric excesses were obtained with bulky aldehydes and for allylstannanes with y-substituents. Pentacoordinated allyltin complexes may be involved97. 

Allylation of aldehydes and ketones by reagents, electrochemically generated at the cadmium anode from allyl bromides, are also known30. 

Chromium(II) Chloride Mediated Addition of Allyl Bromides to Aldehydes General Procedure12 ... 

A mixture of 10 mmol of the allyl bromide and 10-15 mmol of the aldehyde, dissolved in 20 mL of THF, is added dropwise at — 5 to 0°C to the chromium(II) chloride solution in THF prepared by method A or B. The mixture is stirred for 36 h at this temperature and then 15 mL of sat. sodium hydroxide and 20 g of anhyd Na2S04 are added stirring is continued for 20 min at 201C. The mixture is filtered over a pad of Celite/Na2S04 (7 l). The filtrate is concentrated and the residue purified, usually by chromatography on silica gel with pentane/diethyl ether or hexane/ethyl acetate. 

Table 2. 1,2-Disubslituted 3-Butcnols From Chiral Allyl Bromides and Achiral Aldehydes (CrCl3/LiAlH4) 2...

Table 3. 3-Subslituted 1-(a-IIydroxyalkyl)-3-bulcnols from Chiral Allyl Bromides and Chiral Aldehydes (CrCl2)12...

Diene alcohol (38) is the pheromone of the codling moth, tlie creature responsible for the grubs in apples, and of the various possible disconnections (a) is best as it gives most simplification and a stabilised ylid (39) which will produce the requi red trans double bond. Allylic bromide (40) and aldehyde-ester (41) are available,... 

The indium-mediated allylation of trifluoroacetaldehyde hydrate (R = H) or trifluoroacetaldehyde ethyl hemiacetal (R = Et) with an allyl bromide in water yielded a-trifluoromethylated alcohols (Eq. 8.56).135 Lanthanide triflate-promoted indium-mediated allylation of aminoaldehyde in aqueous media generated (i-airiinoalcohols stereoselectively.136 Indium-mediated intramolecular carbocyclization in aqueous media generated fused a-methylene-y-butyrolactones (Eq. 8.57).137 Forsythe and co-workers applied the indium-mediated allylation in the synthesis of an advanced intermediate for azaspiracids (Eq. 8.58).138 Other potentially reactive functionalities such as azide, enone, and ketone did not compete with aldehyde for the reaction with the in situ-generated organo-indium intermediate. 

The type I situation usually gives an antidiastereoselectivity that is independent of the stereochemistry of the double bond in the allyl bromide moiety. The diastereoselectivity (anti/syn ratio) is governed by the steric size of the substituent on the aldehydes. Anti/syn ratio increases as the size of the aldehyde R group or the substituent on the allyl bromide increases (Scheme 8.14). 

A new method has been developed for the synthesis of ( )-3-methyl Baylis-Hillman-type adducts with high E/Z (>93%) selectivity in modest to good yields. The process consists of two steps an indium-mediated allylation reaction and a simple base-catalyzed isomerization step (Eq. 8.61). Various aldehydes were allylated with allyl bromides using indium under very mild conditions in aqueous media and thus converted to the Baylis-Hillman-type adducts.150... 

Pb. Homoallylic alcohols can be obtained from allylation of aldehydes and ketones with allyl bromide promoted by metallic lead in aqueous media.176... 

Sb. Commercial antimony metal, in aqueous 1 M HC1 or DC1 solution, reacts with allyl bromide and aldehydes to give the corresponding homoallylic alcohols in good yield. The reaction proceeds through the formation of allylstibine intermediates.179 The same allylation can be... 

Fe. Iron metal was found to be able to mediate the allylation reactions of aryl aldehydes with allyl bromide using sodium fluoride as the promoter. The formation of an allyliron species was proposed as the reactive intermediate in the reaction (Scheme 8.20).187 In view of... 

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

One of the important new directions in the study of addition reactions of organozinc compounds to aldehydes is the use of ionic liquids. Usually, application of these compounds in reactions with common organometallic reagents has a serious problem ionic solvents are usually reactive toward them, particularly Grignard and organolithium derivatives. It has been recently reported that carbonyl compounds react with allylzinc bromide formed in situ from allyl bromide and zinc in the ionic liquid 3-butyl-l-methylimidazolium tetrafluoroborate, [bmim][BF4].285 Another important finding is that the more reactive ZnEt2 alkylates aldehydes in a number of ionic liquids at room temperature.286 The best yields (up to 96%) were obtained in A-butylpyridinium tetrafluoroborate, [bpy][BF4] (Scheme 107). 

Although both boronates and alanates react with allylic bromides, aldehydes and C02 to afford allenic products in satisfactory yield, the alanates are more efficient in additions to ketones (Table 9.14). Boronate reagents do not require a B-C alkyl migration for their preparation. Thus the starting acetylene possesses the structural elements of the product. Additionally, the issue of dummy ligands is irrelevant. 

Carbanions, generated by the reaction of benzylsilanes with tetra-n-butylammo-nium fluoride react with non-enolizable aldehydes to produce the alcohol [67], When a stoichiometric amount of the ammonium fluoride is used, the methylarene corresponding to the benzylsilane is frequently a by-product and arises from formation of the hydrogen difluoride salt during the reaction. When only catalytic amounts of the ammonium fluoride initiate the reaction, the formation of the methylarene is suppressed. In a similar type of reaction (although the mechanism is not known) between aldehydes and ketones, allyl bromide, and tin in the presence of trimethylsilyl chloride the yield of the but-l-en-4-ol is raised significantly by the addition of tetra-n-butylammonium bromide, particularly in the reactions with... 

Metallic tin, Sn(0), is even more effectively employed. For example, in the presence of Sn(0), allyl bromide and a-halocarbonyl compounds afford nucleophilic organometallic species, which add to aldehydes in good yields to give homoallylic alcohols (12) and g-hydroxycarbonyl compounds (13,14) respectively. a-Diketones could be reduced by activated Sn(0), to give tin(II) enediolates which in turn undergo aldol reaction to form a,g-dihydroxyketones (15,16). This reaction was successfully applied to a stereoselective synthesis of methyl D-glucosaminate (17). 

For the reaction of 1,3-dioxin -ones with electrophiles, activation by deprotonation of the side-chain alkyl group is required. Typically lithium diisopropylamide (LDA) is used as a base. The resulting lithium dienolates react with aldehydes <2002EJ0718> or with allyl bromides in the presence of Ar,Ar -dimethylpropyleneurea (DMPU) <2005AGE820, 2006CEJ2488> exclusively at the side-chain double bond, albeit in modest yields (Equation 25). 

The allylic alcohol 176, prepared by the hydrolysis of allylic bromide 173 <2004JME1423>, was oxidized with MnOz to the corresponding aldehyde 177, which reacted easily with allyl bromide in the presence of zinc under Barbier s conditions to give the adduct 178 (Scheme 25). Of particular note is the fact that the peroxide bridge was not sensitive to Zn under these reaction conditions <20050L5219>. 

The Hiyama addition of allyl bromide 20 to (7 )-2-(methoxymethoxy)hexanal to give 21 with high stereoselectivity. Both the starting allyl bromide and the aldehyde are chiral and were used in nonracemic form. The relative configuration of the two stereogenic centers created in this reaction (c and d) had to be determined128 (see pp 463 and 483). 

---