Aryl and alkenyl boronic acid

Hayashi et al. and Miyaura et al. have reported that far less nucleophilic aryl- and alkenyl-boronic acids can react with a variety of enones in the presence of a BINAP-rhodium catalyst to give adducts with high enantiopurity in general (Scheme 8D.5) [13], The one pot procedure, involving the hydroboration of alkynes as the first step (R = alkenyl), was achieved in the presence of amines without affecting the enantioselectivity [13]. 

The ketone carbonyl of a series of isatins (63) undergoes enantioselective addition of aryl- and alkenyl-boronic acids, using a rhodium catalyst and a chiral phosphine.180... 

A diastereoselective Rh(I)-catalysed conjugate addition reaction of aryl- and alkenyl-boronic acids to unprotected 2-phenyl-4-hydroxycyclopentenone (207) has been investigated. The free OH group on the substrate was found to be responsible for the (g) stereochemistry, which is cis for arylboronic derivatives (208). In the case of the alkenylboronic compounds, the stereochemistry can be tuned to either a cis (with a base as additive) or trans addition (209) (with CsF as additive), without the need for protecting groups.249... 

Suzuki, Stille, and related couplings. The oxidative addition of the C-B bond in aryl and alkenyl boronic acids to Pd(0) initiates the coupling with aryl halides or... 

Oxidations. Cu(OAc)2 has been used as a reoxidant in Pd catalyzed reactions of aryl and alkenyl boronic acids with alkenes and alkynes, and aryltins, and aryl or alkenyl silanols with electron deficient olefins (eq 26). This Mizoroki-Heck type reaction supposedly proceeds through a Pd(II)-boron transmetallation step, followed by addition across the double (triple) bond and final... 

The ability of aryl and alkenyl boronic acids to oxidatively add to Pd(0) was demonstrated by their participation in cross-coupling reactions with alkenes (752). Homocoupled products derived from organoboronic acids have been identified in Suzuki reactions. This reaction was applied to the synthesis of coupled products derived from the homocoupling of organoboroxines (755). 

Rhodium(I)-complexes are known to be excellent catalysts for the conjugate additions of aryl- and alkenyl boronic acids to a,/3-unsaturated ketones, esters and amides [73,74]. Batey has recently prepared aryl and alkenyl trifluoroborates as air-and moisture-stable reagents for the nucleophilic addition to enones in the presence of a Rh(I)-catalyst to give /3-functionalized ketones in good yields [75]. A number of aryl fluoroborates with electron-withdrawing substituents were also tolerated in this reaction. An unprecedented Rh-catalyzed 1,4-addition of aryl boro-... 

Alkenyl, aryl, and heteroaryl boronic acids reacted with 1,2-diamines and glyoxylic acid giving directly piperazi-nones (Equation (123)).571 2-Hydroxymorpholines were synthesized from glyoxal, 2-aminoethanols, and aryl- or 1-alkenylboronic acids (Equation (124)).572... 

N-l-Substituted iodoimidazoles behave normally with arylboronic acids to give cross-coupled products <2005T6056>. N-l-Substituted-2-bromoimidazoles also coupled efficiently with aryl boronic acids and alkenyl boronic acids to give cross-coupled products in high yields (Scheme 95) <2004JOC8829>. 

CuTC also promotes the nonbasic version of the Suzuki cross-coupling. It was observed that both aryl and alkenyl iodides reacted smoothly with a variety of aryl, heteroaryl, and alkenyl-boronic acids in the presence of a Pd catalyst and an equivalent of CuTC at room temperature (eq 20). Bromo, chloro, and triflate derivatives failed to couple. 

Finn and Petasis have independently shown that salicylaldehyde is a suitable aldehyde for the Petasis borono-Mannich reaction, with alkenyl, aryl and heteroaryl-boronic acids (Equation 6) [30, 31]. The reaction works best for aliphatic secondary amines, as in the formation of 41 primary amines give modest yields of adducts 41. Benzaldehydes lacking ortho hydroxyl functionality do not react, with even ortho methoxy functionality being unsuitable, which is consistent with a tethering mechanism via putative intermediate 9 (Figure 7.3). Petasis and Boral reported that reactions occurred at room temperature over 24-36 h, using EtOH, MeOH or acetonitrile. 

Carboxylations of C-B and C-H bonds have been performed by copper(I)-NHC complexes in the presence of carbon dioxide. This reaction has been carried out on a range of aryl- and alkenyl-boronic derivatives as well as on alkylboranes. The C-H carboxyla-tion has been somehow restricted to the most acidic hydrogen of azoles and benzazoles. 

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

The palladium-catalyzed coupling of boronic acids with aryl and alkenyl halides, the Suzuki reaction, is one of the most efficient C-C cross-coupling processes used in reactions on polymeric supports. These coupling reactions requires only gentle heating to 60-80 °C and the boronic acids used are nontoxic and stable towards air and water. The mild reaction conditions have made this reaction a powerful and widely used tool in the organic synthesis. When the Suzuki reaction is transferred to a solid support, the boronic add can be immobilized or used as a liquid reactant Carboni and Carreaux recently reported the preparation of the macroporous support that can be employed to efficiently immobilize and transform functionalized arylboronic adds (Scheme 3.12) [107, 246, 247]. 

The transformation of lithio derivatives of dibenzothiophene into alkyl, alkenyl, hydroxyalkyl, formyl, acetyl, carboxylic acid, alkyl and arylsilyl, boronic acid, aryl and carbinol derivatives of dibenzothiophene is dealt with in the appropriate sections. In addition, the four mono-tritio derivatives of dibenzothiophene have been prepared from the corresponding lithio derivatives via hydrolysis with tritiated water (Section III, 0,2). ... 

The use of alkenyl boronic acid derivatives 50, which are readily prepared via hydroboration or bromoboration of alkynes, affords the corresponding p,y-unsaturated amino acids (e.g. 52-57) in a geometrically pure form [34], A variety of amines 48, including primary and secondary amines, anilines, amino alcohols and hydroxylamines can effectively participate in this process, while the alkenyl boronic acid can contain alkyl, aryl or bromo-substituents. Although the alkenyl amino acid side chain is introduced through the boronic acid component, the use of more substituted a-keto acids 49 allows the simultaneous incorporation of an additional a-substituent (e.g. 57). 

These boronic esters are easily hydrolyzed to give frara-alkenylboronic acids with complete retention of their stereochemistry (C in Figure 13.10). Alkenylboronic esters and alkenylboronic acids are organometallic compounds that can be alkenylated and arylated in Pd-catalyzed reactions (Section 13.3.2). Aside from this, the fram-alkenyl-boronic acid esters as well as the frara-alkenylboronic acids are valuable precursors of haloalkenes (Figure 3.10). 

Synthetically attractive arylation and alkenylation of a-bromoalkenyl phosphonates (471) with organo-boranes and -borates have been performed. Arylation was successful with the aryl boronic acids and a palladium catalyst, while alkenylation proceeded best with alkenyl borates, and a nickel catalyst (Figure 87). ... 

Palladium chemistry has been utilised to introduce aryl groups to a furan a-position by substitution of hydrogen, and via boronic acids, and in Heck-type alkenylations, again at C-2, via oxidative type palladation (cf. section 2.7.2.1). 

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