Borates alkynyl, reactions

Lithium alkynyl(trialkoxy)borates have also been found suitable partners for this reaction, and have been success-fully coupled with aryl bromides, iodides, and allyl carbonates. Molander recently reported on the coupling of alkynyltrifluoroborates with aryl bromides, triflates, and chlorides in moderate yields using Pd(dppf)Gl2 as catalyst and GS2GO3 as base, in THF or water at 60... 

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... 

The reaction of -butyl tellurium bromide with alkynyl borates 112 is used to prepare (A )-vinvlic tellurides 113 as shown in Scheme 67.1... 

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. 

The reactions of bis(alkynyl)metallocenes Cp2M(C=CR)2 (M = Zr, Hf R = Me, Pr11, Bu11, Gy) with B(C6F5)3 afford the corresponding metallocene borate betaines of structure type 760.586 An assumed intramolecular alkyne insertion reaction leads to their less stable methylenecyclopropene-derived isomers, which are effectively trapped by the added / /7-butylisocyanide to yield complexes 764 which contain a methylenecyclopropene derived [Pg.906]

Heterocycles. Alkenyl and aryl boronates deliver their organic residues to the opposition of the nitrogen atom of cyclic carbinolamines to replace the hydroxyl group. Synthesis of 2,3,5-trisubstituted furans, from a catalyzed reaction of alkynyl borates and enones, is achieved in one step. 

Scheme 5.2-117 The Mannich reaction with alkynyl borates in [BMIM][BF4] [262].

A section on alcohol-forming reactions is included in a recent review of organo-bocates (such as cyano-, alkenyl-, and alkynyl-borates) in organic synthesis. 

Another reaction between alkynes and CO using alkali metals yields a,3-unsaturated acids. Starting from alkynyl lithium, the lithium trial kylalkynyl borates can be prepared, which react with CO yielding the lithium salt of an unsaturated acid. After further treatment with acetjc acid the stereospecific ., p-unsaturated acids are obtained in yields of about 70-80 % [97] (Figure 34). For instance, trihexylbo-rane and hexynyl lithium led to 2-butylnonenoic acid in yields of 83 %. 

The Suzuki coupling was developed by Professor Akira Suzuki of Hokkaido University. The Suzuki coupling uses a boron compound (R-BYj) and an alkenyl, aryl, or alkynyl halide or triflate (RX) as the carbon sources, with a palladium salt as the catalyst. Bromides and iodides are the most commonly used halides chlorides are less reactive. Alkyl halides can sometimes be used but are subject to elimination. A base is also required. The boron compound can be a borane (R jB), a borate ester (R B(OR)2), or a boric acid (R B(OH)2), where R is alkyl, alkenyl, or aryl. The general reaction is shown in the following scheme, where X is halide or triflate and Y is alkyl, alkoxyl, or OH. A list of the types of components that can be used is given in Table 24.1. This reaction is one of the principal methods now used to prepare biaryls. 

The Schaus group also reported related reactions involving asymmetric allyl-boration of acyl imines [59], asymmetric three component Petasis condensation reaction of secondary amines/glyoxylates/alkenyl boronates [60], as well as addition of aryl, vinyl, and alkynyl boronates to acyl imines (Fig. 15) [61]. In the later reaction, a two point coordination transition state was proposed to account the observed facial selectivity. 

Alkynyl boronic acid derivatives were not used earlier in Suzuki couplings. An effective Suzuki-Miyaura reaction between alkynyl ate complexes (alkynyltrialk-oxy borate complexes) has been reported by Colobert [112] Oh [113]. 1-Alkynyl(trii-sopropoxy) borates (137) were prepared by borylation of the corresponding alkynyl lithium species. These stable borate complexes were subsequently used in Suzuki coupling leading to products of type 138 (Scheme 3.74). 

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