Boronate group

Unsaturated compounds containing both a double bond and a charactensbc group such as hydroxyl, carbonyl, or nitnle or an organophosphorus, -selenium sulfur, -iodine, or -boron group are also included in this section even when only the double bond IS oxidized... 

Formation of group-IIIB-group-IB and -IIB element bonds is limited almost exclusively to the element B and is observed predominantly in metalloboranes and metallocarboranes. The boron-IB and boron-group-IIB bonding interactions either are of the a type or can be described as multicenter bonds ... 

The formation of boron-group IB bonds succeeds in two ways by transfer of a boryl group from metal-boron compounds to other metals, and by reaction of anionic boranes or carboranes with transition-metal halides. 

The synthesis of compounds containing boron-group IIB bonds also occurs by two pathways. The most convenient method is using anionic borane or carboranc species, as in the group-IB case, to react with Zn, Cd, or Hg halides. Moreover, reactions between organometallic compounds (Zn, Cd) with unchanged boranes arc also realized, so Zn and Cd decaboranes, e.g., MB H 2 n solvent (M = Zn, Cd), result from reactions of decaborane(14) with MRj . 

This provides a mechanism for migration of the boron group along the carbon chain by a series of eliminations and additions. 

The activating capacity of boronate groups can be combined with the ability for facile transesterification at boron to permit intramolecular reactions between vinyl-boronates and 2,4-dienols. 

The Boron Group (Metallics to Semimetals) Periods 2 to 6, Group 13 (IIIA)... 

The boron group (group 13 IIIA) consists of the elements boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Ti). All have three electrons in their outer valence shell. A few exhibit metal-like characteristics by losing one or more of their outer electrons. For example, aluminum can lose one or three of its valence electrons and become a positive ion just as do other metals, but other elements in this group have characteristics more hke metalloids or semiconductors. 

Hydroboration is thermally reversible. At 160°C and above, B—H moieties are eliminated from alkylboranes, but the equilibrium is still in favor of the addition products. This provides a mechanism for migration of the boron group along the carbon chain by a... 

The direct cycloaddition adduct was oxidized, resulting in the hydroxylated isoxazoline product (316). Better selectivities were obtained in 1,3-dipolar cycloadditions of 204 with nitrile oxides (317,318). The 1,3-dipolar cycloadditions proceeded with concomitant loss of the boron group to give the isoxazoline products in up to 74% ee (318). The alkene 204 was also tested in reactions with nitrones. The reactions proceeded with poor yields, but high selectivities were observed in two cases (318). Gilbertson et al. (319) investigated the use of chiral ot,p-unsaturated hexacarbonyldiiron acyl complexes 205 as dipolarophiles in reactions with nitrones. Selectivities of up to >92% de were observed. The iron moiety was removed oxidatively after the cycloaddition and the thioester was hydrolyzed. 

Maternal blood boron concentrations were elevated in all boron groups in a dose-dependent manner. On gestational day 20, blood B concentrations of 1.3 mg/kg FW were associated with the no-observed-adverse-effect level (NOAEL) and 1.53 mg/kg FW with the lowest-observed-adverse effect level (LOAEL), equivalent to dietary intakes of 10 and 13 mg B/kg BW daily, respectively, for developmental toxicity. Developmental toxicity persisted postnatally only at 25 mg B/kg BW daily, a dose associated with more than a 10-fold increase in maternal blood B (2.8 mg B/kg FW) vs. 0.23 mg/kg FW in controls (34)... 

The work by Armstrong was extended to include the room temperature resin capture of trisubstituted ethenes with a pendant boronate group.80 Modification of the amide linker above to a novel silyl-based one allowed for the traceless cleavage of superior analogues. 

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