Crotyl bromide

Crotyl bromide [29576-14-5] M 135.0, b 103-105 /740mm, n s 1.4792. Dried with MgS04, CaC03 mixture. Fractionally distd through an all-glass Todd column. [Todd column. A column (which may be a Dufton type, fitted with a Monel metal rod and spiral, or a Hempel type, fitted with glass helices) which is surrounded by an open heating jacket so that the temperature can be adjusted to be close to the distillation temperature (Todd Ind Eng Chem (Anal Ed) 17 175 1945)]. 

Jackson and Smith further showed that crotyl bromide reacts with 3-methylindole magnesium iodide to give a mixture of products from which l- i-butyl-3-methylindole (45) and 2-w-but5d-3-methylindole... 

The multi-component procedure is also effective for the chromium-catalyzed addition of organic halides to aldehydes (the Nozaki-Hiyama-Kishi reaction) [73]. The active Cr(II) species is recycled by redox interaction with Mn powder as the stoichiometric co-reductant in the presence of MesSiCl (Scheme 34), which mainly liberates the chromium catalyst from the alkoxide adduct. The chemo- and diastereo-selective addition reaction is performed with a variety of organic halides and alkenyl triflates. In the case of crotyl bromide, the addition is highly stereoconvergent, i.e., the respective anti-... 

The reaction of crotyl bromide with ethyl diazoacetate once again reveals distinct differences between rhodium and copper catalysis. Whereas with copper catalysts, the products 125 and 126, expected from a [2,3] and a [1,2] rearrangement of an intermediary halonium ylide, are obtained by analogy with the crotyl chloride reaction 152a), the latter product is absent in the rhodium-catalyzed reaction at or below room temperature. Only when the temperature is raised to ca. 40 °C, 126 is found as well, together with a substantial amount of bromoacetate 128. It was assured that only a minor part of 126 arose from [2,3] rearrangement of an ylide derived from 3-bromo-l-butene which is in equilibrium with the isomeric crotyl bromide at 40 °C. 

The Rh2(OAc)+-catalyzed reaction between crotyl bromide and ethyl diazoacetate at or below room temperature follows the pathway 129 - 131 - 132 exclusively. At higher temperature, when ethyl bromoacetate and increasing amounts of the [1,2] rearrangement product 126 are found additionally, the 129 -> 130 - 132 -f 133 route becomes a competing process. With copper catalysts, this situation may be applicable at all temperatures, but it has been suggested that the route via complex 130 operates solely, when copper bronze is the catalyst154). 

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... 

Crotononitrile, b482 trans-Crotonyl alcohol, c311 Crotyl alcohols, b486, b487 Crotyl bromide, b276 Crotyl chloride, c79... 

While the intramolecular Heck reaction has been widely used to synthesize indoles and benzofurans, not many applications have been found in the preparation of benzothiophenes because of the thiophilicity of the Pd(II) species. Pleixats and coworkers treated iodophenylsulfide 151, obtained from o-iodoaniline and crotyl bromide in two steps, with... 

The enantioselective lithiation of anisolechromium tricarbonyl was used by Schmalz and Schellhaas in a route towards the natural product (+)-ptilocaulin . In situ hthi-ation and silylation of 410 with ent-h M gave ewf-411 in an optimized 91% ee (reaction carried ont at — 100°C over 10 min, see Scheme 169). A second, substrate-directed lithiation with BuLi alone, formation of the copper derivative and a quench with crotyl bromide gave 420. The planar chirality and reactivity of the chromium complex was then exploited in a nucleophilic addition of dithiane, which generated ptilocaulin precnrsor 421 (Scheme 172). The stereochemistry of componnd 421 has also been used to direct dearomatizing additions, yielding other classes of enones. ... 

Again, cobalt hydrotricarbonyl probably adds initially. The addition could be either a 1,4-addition or a 1,2-addition in which cobalt initially adds to the second carbon atom of the diene, and then undergoes an allylic rearrangement. The 3-pentenoylcobalt tricarbonyl triphenylphosphine prepared in this manner contains considerably more of the cis isomer than the same compound prepared from trans crotyl bromide and sodium cobalt tetracarbonyl. This, indicates that the hydrocarbonyl prefers cis addition (47). 

It is a colorless liquid with an oily-fruity odor with floral, petal-like notes. For synthesis, 1,3-cyclohexanedione is reacted with crotyl bromide in the presence of potassium hydroxyde to give the 2-alkenyl-substituted 1,3-diketone. Ring cleavage with sodium hydroxyde leads to the unsaturated keto acid which is reduced with NaBH4 under formation of the title compound [201]. 

Cobalt carbonyl hydride, [Co(CO)4H], when treated with butadiene gives a mixture of two isomeric compounds [Co(C4H7)(CO)3] (6,128,165). The same mixture of isomers is formed when Na[Co(CO)4] is treated with crotyl bromide, i.e., a l-bromobut-2-enc/3-bromobut-l-enc mixture (109). These two compounds, [Co(C4H7)(CO)3], have been shown by their nmr spectra to be the two geometrical isomers (XLIII) and (XLIV) of 7r-cro ty 11 ri car bo n y 1 co halt (165). 

Crotyl bromide [29576-14-5] M 135.0, b 103-105°/740mm, CaCO3 mixture. Fractionally distd through an all-glass Todd column. 

Homoallylic alcohols (8, 111-112). The high rltreo-selectivity observed in the reaction of benzaldehyde with crotyl bromide (either irons or cis) is general for relatively unhindered aldehydes (equation I). High threo selectivity is still observed in the reaction with an a-methyl substituted aldehyde, but a-asymmetric induction (at C3) is rather low (2.2 1) with simple aldehydes (equation II).1... 

Acetyl chloride Morpholine Acetic acid Sodium hydoxide Sulfuric acid Crotyl bromide... 

In a flask there are charged sodium hydride titre 80% and benzene. Keeping temperature 20-30°C a solution of ethyl 4,4 -biphenylacetate and of crotyl bromide in dimethylformamide is dropped during 30 min in the flask. Then the reaction mixture is heated under reflux for 2 h, and subsequently cooled to 10°C. Thereafter H20 are charged and mixture stirred 15 min. Two phases separate. Organic phase is washed with H20 and dried. The dried solution is concentrated under vacuum till an oily residue consisting of ethyl ester of diphenesenic acid. 

The reaction of benzaldehyde with unsymmetrical allylic bromides in the ionic liquid bmim also proceeds regioselectively to realize a carbon-carbon bond formation at the more substituted allylic carbon (Scheme 5). In the coupling of crotyl bromide with benzaldehyde, the product is a nearly 50 50 mixture of antilsyn diastereomers. Cinnamyl bromide predominantly gives the //-diastereomer. The regio- and diastereoselectivity is similar to that observed for these in aqueous media.104... 

The indium-mediated aqueous Barbier-type reaction of crotyl bromide with benzaldehyde shows no diastereo-selectivity. However, the use of preformed crotylindium sesquibromide in DMF affords. sy/z-l-phenyl-2-methyl-3-buten-l-ol (ca. 40% de) after aqueous acidic workup. At 22 °G in DMF prior to workup, a greater relative proportion of //-intermediate is decomposed as compared to its yy/z-diastereomer. The resultant kinetic diastereoselection upgrades the syn anti ratio to 99 1 with a concomitant drop in overall yield (Scheme 14).127... 

The coupling addition of crotyl bromide to a triad of conformationally unrestricted a-oxy aldehydes in water, aqueous THF, and anhydrous THF has been examined. The proportion of. sy/z-isomers reaches a maximum (syn anti = 5.6 1) when the neighboring hydroxyl group is unprotected and water is the reaction medium (Scheme 33). Crotyl bromide adds to the hydroxy aldehyde with a preference for the adoption of the cyclic chelated transition states 31 and 32 (Scheme 34). 

Even the secondary system we also considered is in rapid equilibrium when the leaving group is bromide. This time both allylic isomers are present, and the primary allylic isomer (known as crotyl bromide ) is an EiZ mixture. The bromides can be made from either alcohol with HBr, and the same ratio of products results, indicating a common intermediate in the two mechanisms. You saw at the beginning of Chapter 17 that this reaction (Chapter 16) is restricted to alcohols that can... 

Except for protic and Lewis acids, other electrophilic reagents can also promote the aliphatic 3-aza Cope rearrangement. In fact, the first example of a [3,3]-sigmatropic rearrangement of 7V-allylenammonium salt may date back to the early 1960s102. When enamine 152 reacted with crotyl bromide at 80 °C, it gave after hydrolysis 2,2,3-trimethyl-4-pentenal (153) rather than 2,2-dimethyl-4-hexenal (equation 32). 

Allyl a-D-galactopyranoside Acetal Toluene TBAI 60 Crotyl bromide 0 >61 0 200... 

The earliest report on the Claisen rearrangement of allyl ethers in the pyridine series was by Saltzer et ai.4 Reaction of 2,6-dimethyl-4-pyridone with allyl bromide and crotyl bromide was assumed to give... 

The mechanism of copper catalysis is obviously related to the halogcnaiing properties of the copper salts the activity is restricted to the halides, CuCN, CuOAc, CufOjSCFa) and CuF being inactive. The addition of halide ions, BrCN or croiyl bromide to CuCN, however, restores an activity comparable to CuBi efficiency. Crotyl bromide is a particularly efficient additive and may be an intermediate in the process. The rate increases by a factor of three in relation to the neat CuBr catalyzed reaction. Yields Itigher than 90% can thus be obtained. Similarly. UBr reactivates the catalyst 16). 

A recent variation of this strategy is due to Ziegler, who used TMS ethers of cyanohydrins of (x, -unsaturated aldehydes as substrates. Alkylation with an allylic halide, such as crotyl bromide in equation... 

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