Branched bromo

Fu s group showed more recently that ot-bromo ketones 6b can be coupled with arylzinc halides catalyzed by 5 mol% NiCl2 DME and 6.5 mol% of PyBOX ligand 5e with good asymmetric induction providing benzylic ketones in 71-93% yield and 72-96% ee (entry 12) [54]. The lower ee values were obtained with orf/io-substituted aryl bromo ketones, while orf/to-substituted arylzinc reagents as well as a-branched bromo ketones did not react. 

Figure 9 Compared molar mass distributions of regular and star-branched bromo-butyls. (From Ref. 65.)...

Isobutylene-based elastomers include HR, the copolymer of isobutylene and isoprene, halogenated HR, star-branched versions of these polymers, and the terpolymer isobutylene-p-methylene styrene-bromo-p-methyl styrene (BIMS). A number of recent reviews on isobutylene-based elastomers are available [33-35]. 

Reduction of 2-bromo-3-pentanone at mercury affords a mixture of 3-pentanone and l-hydroxy-3-pentanone, whereas electrolysis of Q ,Q -dibromoacetone in the presence of benzoate gives a mixture of products arising from both a carbon-bromine bond cleavage and an Sn2 displacement of bromide by benzoate [94]. In an acetic acid-acetate buffer, branched dibromo ketones, such as 2,4-dibromo-2,4-dimethyl-3-pentanone, are reduced to a-acetoxy ketones however, less highly substituted compounds, such as 4,6-dibromo-5-nonanone, undergo simple cleavage of both carbon-bromine bonds [95]. Other work dealing with the reduction of Q, Q -dibromoketones has been described [96]. 

Haloalkanes can be regarded as substituted alkanes in which one or more of the hydrogen atoms is replaced by a halogen atom. They are named in a similar fashion to branched-chain alkanes with the halogen atoms treated like branches. For example, the anaesthetic halothane has the structure shown in the diagram and is called 2-bromo-2-chloro-l,l, 1-trifluoroethane. 

Unsaturated branched-chain sugars were synthetized with 72-84 % yield from both protected and unprotected 2-bromo-D-glucal with methyl acrylate in CH3CN/H2O 5/1 or in DMF/H2O 5/1 with a catalyst prepared from [Pd(DBA)2] and P(o-tolyl)3. Et3N or K2CO3 + /1-BU4NHSO4 could be used as base with similar results. 

The boiling points of Isomeric haloalkanes decrease with increase In branching (Unit 12, Class XI). For example, 2-bromo-2-methylpropane has the lowest boiling point among the three Isomers. 

Several examples of a new and simple "LEGO" system to obtain thienyl substituted 2,6-oligopyridines <99T5047>, 4-stannyl-, 4-bromo-oligopyridines and branched oligopyridines <99T5067>, staimylated bipyridines and terpyridines <99EJOC313> from... 

Attachment of a suitable branch to the C-3 position125 was achieved by applying known methods resorting to 1,2-dibromoethyl ethyl ether204 and (bromomethyl)-chlorodimethylsilane.205,206 In this way, 1,5-anhydro-3- O-(2-bromo-1 -ethoxy-ethyl)-2-deoxy-4,6- O-isopropylidene-D-araWno-hex-1 -enitol (67), 1,5-anhydro-... 

Other useful double-ended chiral synthons can be readily derived from derivatives of commercial methyl 3-hydroxy-2-methylpropanoate enantiomers (Figure 8.3B). Even more convenient, both enantiomers of 3-bromo-2-methyl-l-propanol (Figure 8.3B) are commercial products that can be protected at the alcohol function, chain extended on the other side, then deprotected and the resulting alcohol converted to a halide or sulfonate for a second alkylation (e.g., Fukaya et al., 1997 Schlamp et al, 2005). We have used these synthons to efficiently generate both enantiomers of three long-chain methylalkanes (J.G.M., unpublished data). Another useful double-ended methyl-branched synthon can be readily derived from enantiomers of 3-methylbutyrolactone (Figure 8.3B) (Mori, 2008a). 

Brunner and Fiirst[431 reported the synthesis of a series of optically active, extended chelate phosphines, one of which was derived from the reaction of 5-bromo-l,3-di(bor-neoxymethyl)benzene (69) and bis(dichlorophosphino)methane (70). Technically, the product (-)-l,l-bis 3, 5 -di(borneoxymethyl)phenyl]phosphino methane (71) is both a first tier P- and 1,3-aryl-branched dendrimer. Excluding distortions, the maximum distance between the P atom and the most distant H atom(s) is 11.9 A for the two-layer ligand 71. The Rh-catalyzed [Rh(cod)Cl]2) hydrogenation of (a)-/V-acetamidocinnamic acid in the presence of 71 afforded a disappointingly low [5.2 % ee (/ )] optical induction. 

Allylindium reagents bearing substituents at the 7-position react with carbonyl compounds in organic and aqueous media regioselectively at the 7-position, via a six-membered transition state, to afford the corresponding branched homoallylic alcohols, if no sterically bulky carbonyl or allyl substituent is involved.102 For example, the indium-mediated reaction of aldehydes with 3-bromo-l-cyano-l-propene proceeds readily in water to give cr-cyano-f3-ethylenic secondary alcohols (Scheme 4).103... 

Allylindium, generated by transmetallation of 5-benzyloxy-4-methyl-2-pentenyl(tributyl)stannane, reacts with benzaldehyde leading to the l,5-< /z//-CE)-stereoisomer with a useful level of 1,5-stereoinduction (Equation (13)).151 2-C-branched sugars and C-disaccharides are prepared diastereoselectively by the indium-mediated reaction of 4-bromo-2-enpyranoside (Equation (14)).152... 

The thermal fade rates of 6-nitroBIPS and its 8-bromo, 8-iodo, and 8-methoxy derivatives were measured in 13 solvents of varying polarity. Plotting the log of the rate constants vs. the ET values of the solvents gave linear plots, not double-branched ones as found later by this research group. The ring closure involves a zwitterionic transition state. Semiempirical molecular orbital (MO) calculations predict that the most stable merocyanine configuration is the cis-trans-trans-cis form.121122... 

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