Methoxy borate complexes

Alkynyl(methoxy)borates prepared in situ from an alkynyllithium or sodium and 9-methoxy-9-BBN coupled with 1-alkenyl and aryl halides (Equation (210)).899-902 Addition of triisopropylborate to lithium acetylide yielded an air stable and isolable ate complex that couples with aryl and alkenyl halides (Equation (211)).903 904 Air and moisture stable alkynyltrifluoroborates were probably the most convenient reagents that allow handling in air and coupling reactions in basic aqueous media (Equation (212)).46... 

Alkynylboranes as useful synthetic intermediates are stronger Lewis acids and are easily hydrolyzed compared with alkylboranes. The Pd-catalyzed reaction of stable methoxy(alkynyl)borate complexes 71 derived from alkynyllithium gives arylacetylenes and stereodefined enynes 72 efficiently [Eq. (27)] [40]. 

Suzuki couplings. Pd-catalyzed reactions of B-allyl borate complex derived from 6-methoxy-9-borabicyclo[3.3.1]nonane with aryl triflates give allylarenes. This technique broadens the scope of the Suzuki coupling to allow transfer of Me, TMSCHj, and alkynyl groups which has eluded conventional manipulations. 

A few studies have been carried out on coupling of alkynyl borones. The stable methoxy(alkynyl)borate complex 158 was prepared in situ by the treatment of B-methoxy-9-borabicyclo[3.3.1]nonane (157) with alkynyllithiums or potassium reagents, and used directly for the coupling with halides to afford a variety of the disubstituted alkynes sueh as 159 [72,73]. 

Iron pentacarbonyl and l-methoxy-l,4-cyclohexadiene react as shown by Birch and oo-workera, but in dibutyl ether this solvent has been found superior. The tricarbonyl(methoxy-l,3-cyclohexadiene)iron isomers undergo hydride abstraction with triphenylmethyl tetrafluoro-borate to form the dienyl salt mixture of which the 1-methoxy isomer is hydrolyzed by water to the cyclohexadienone complex. The 2-methoxy isomer can be recovered by precipitation as the hexafluoro-phosphate salt. By this method the 3-methyl-substituted dienone complex has also been prepared from l-methoxy-3-methylbenzene. The use of the conjugated 1-methoxy-1,3-cyclohexadiene in Part B led to no increase in yield or rate and resulted chiefly in another product of higher molecular weight. An alternative procedure for the dienone is to react tricarbonyl(l,4-dimethoxycyclohexadiene)iron with sulfuric acid. ... 

The two-substituted-Quinazolinap-derived rhodium complexes proved extremely efficient catalysts for the hydro-boration-oxidation of vinylarenes (Table 6). For styrene derivatives, in most cases quantitative conversions were obtained after just 2 h at the relevant temperature (entries 1-6). Higher enantioselectivities were afforded with a 4-methoxy substituent (up to 95% ee, entry 3) compared to the 4-chloro or unsubstituted styrene analogs (entries 5 and 1), a trend also observed in hydroboration with rhodium complexes of QUINAP 60. This highlights that both the electronic nature of the substrate combined with the inherent steric properties of the catalyst are important for high asymmetric induction. It is noteworthy that in most cases, optimum enantioselectivities were afforded by the... 

The ate complex prepared from B-methoxy-9-BBN and Bu3SnLi [24] adds under copper(I)-catalyzed reaction to 1-alkyne to yield exclusively or predominantly lithium [2-tri-n-butylstannyl-(Z)-l-alkenyl]-l-borates [25]. These borates are selectively coupled in the presence of organopalladium or organo-cuprate with a variety of electrophiles (Chart 24.5), exclusively at the vinylcar-bon-boron bond to form a carbon-carbon bond (Table 24.8) [25]. The process is extremely versatile, as various functional groups are tolerated. However, an alkene with opposite regiochemistry (entry K, Table 24.8) [25] is obtained when BF,-Et,0 is added to the initial reaction, which is then refluxed. 

The bidentate bis(pyrazolyl)methane and bis(pyrazolyl)borate ligands, as well as tridentate tris(pyrazolyl)methane and tris(pyrazolyl)borate ligands, also form Pt complexes with the ligand formed by addition of a methoxy group to cod 414-417. 2... 

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