Boronate exchange

Successful syntheses of monoannulated borepins were achieved by Ashe and co-workers by tin-boron exchanges with the tin heterocyclic precursors.105 106 Particularly informative were the properties of 113, which has no benzoannulation (Eq. 34) ... 

It is also possible to perform a zinc-boron exchange if trimethylborate is added to the cyclopropylzinc species (equation 36) °. However, the presence of a zinc alkoxide... 

In addition, if this reaction was run in the presence of trimethylborate, a usual zinc-boron exchange led to the cyclopropylboron derivative that could be used in Suzuki coupling to give rise to trisubstituted cyclopropanes (equation 64) . 

Monobenzo fused borepins have been prepared by tin-boron exchange reactions (equation 18). Different stabilities to air were noted (208 R = OH) was air-sensitive <7lCC29l), but (208 R = Ph) had an unusual stability (67TL1263). 

PBs featuring para-phenylene spacers have also been prepared. Marder reported the synthesis of derivative 16a (related to the ethynyl-bridged compound 5a) by bromine-lithium-boron exchange... 

Using the bromine-lithium-boron exchange strategy, Muller and Lachmann reported in 1993 a series of MPB, DPB, and TPB 27-29 (Scheme 20) All of these compounds were isolated by crystallization and characterized by IR, multinuclear NMR (aH, 13C, 31P, and 11B), and elemental analysis. The presence of P-B interactions was spectroscopically apparent and monomeric closed structures were authenticated crys-tallographically for 27 and 28 (see Section III). 

Aluminum-alkynyl covalent bonds, characteristics, 9, 249-250 Aluminum-aluminum bonds in A1(I) compounds, 9, 261 in Al(II) compounds, 9, 260 Aluminum aryloxides, reactivity, 9, 254—255 Aluminum(III)ates, in organic group-selective transfers, 9, 279 Aluminum(I)-boron bonds, characteristics, 9, 263 Aluminum(III)-boron exchange, process, 9, 266 Aluminum-calix[4]arene catalyst, for alternating epoxide-CC>2 co-polymerization, 11, 617... 

The compound is thermally unstable at room temperature and has an extrapolated boiling point of 27°. Boron exchange is observed with diborane(6) enriched in boron-10 109) and the SH proton exchanges with deuterium chloride 109>. The presence of the mercapto-group in the bridging position is unequivocally established by the boron-11 nmr... 

Tin boron exchange reactions provide a convenient route to diborylated acetylene (equation 33). Diborylalkynes show an enhanced Lewis acidity in comparison to dibory-laUcanes as demonstrated by the coordination of THF in (31), but a lack of binding to the related alkyldiborane (32). This effect has been attributed to the stronger inductive electron-withdrawing effect of sp-hybridized relative to sp -hybridized carbons. ... 

X = S, O, NR). Lithium-, sihcon, or tin boron exchange provide facile access to the desired borylated species. On the other hand siloles and stannoles (X = Si, Sn) with organoboron substituents in the 3-position are conveniently prepared via organoboration reactions. Another new... 

Although ring-annulated and highly substituted borepins have been known for some time, simple 1-substituted borepins have only been thoroughly studied over the past decade. The discovery of a facile synthetic ronte to 1-snbstituted borepins through tin-boron exchange has much opened up the chemistry of these 7-membered boracycles. The chloro-substituted borepin (145) serves as a highly useful precursor to many other borepin derivatives via substitution reactions with nucleophiles (Scheme 20). In addition, several transition metal complexes of 1-borepins have been reported. 

So far the important results of the isotopic-exchange experiments may be summarized as follow s S3) (a) Exchanges occur in which BHi remains an entity, as in the B2H6 self-exchange the rate of deuterium exchange is three times the rate of boron exchange, (b) Exchanges occur... 

Silicon/boron exchange. For the sake of increasing reactivity in coupling an alkenylsilane is converted to a boronate by reaction with BCI3 and then with catechol. Such a product can be used in Suzuki coupling. 

Alternative enolization method. Other methods of enolate generation could well be of use in reducing the reagent quantities. We examined firstly generating the lithium enolate with LDA and then carrying out a lithium-boron exchange. In a model system, this worked well, as... 

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