Diboronic preparation

In this context, an internally activated, sp -sp -hybridized diboron compound, PDIPA diboron (pinacolato diisopropanolaminato diboron) prepared by Santos et al, has shown to easily interact with CuCl salts to favor the B-B cleavage and form the corresponding Cu-Bpin species (Scheme 44) which were very active in the copper-catalyzed, P-borylation of a,P-unsaturated conjugated compounds and aUenoates. " ... 

In a classical multi-step route the critical point is to conduct (he ring closure quantitatively and regioseleclively. In the synthesis of I.PPP, the precursor polymer 13 is initially prepared in an aryl-aryl coupling from an aromatic diboronic acid and an aromatic dibromoketone. 

A different approach to the preparation of boron macrocycles can be made by using diboronates 69-71 for the construction of the macrocyclic derivatives... 

Diboron compounds with alkylamino or alkyloxy substituents are prepared from the appropriate halogenoborane derivative using active metals " ... 

The widespread use of aryl boronic acids or aryl boronates in various metal-catalysed C-C bond-forming reactions has created a substantial demand for these versatile nncleophiles. A general procedure for the preparation of these compounds, based on a NHC/Pd catalysed coupling, has been reported by Fiirtsner and co-workers nsing aryl chlorides and the tetraalkoxy diboron derivative 27 as conpling partners. Very good yields were obtained in several cases especially when electron poor aryls were employed [169]. Milder reaction conditions can be achieved when diazonium salts are used instead of chlorides [170] (Scheme 6.51). 

The direct preparation of arylboronic esters from aryl halides or triflates now allows a one-pot, two-step procedure for the synthesis of unsymmetrical biaryls (Scheme 1-41) [147]. The synthesis of biaryls is readily carried out in the same flask when the first coupling of the triflate with diboron 82 is followed by the next reaction with another triflate. The synthesis of naturally occurring biflavanoids and the couphng of N-(phenylfluorenyl)amino carbonyl compounds to polymeric supports are reported [154]. 

Diboron tetrahalides, B2X4, are also known. These may be prepared in a variety of ways, among them the reaction of BC13 with mercury. 

The Stille coupling was also employed successfully to prepare covalently bound DNA base-pairs. 1,4-, and l,3-bis(stannyl)benzenes were used to connect purine units covalently through a phenylene linker. The reactions gave the desired products in mediocre yield, along the by-products of destannylation and mono-coupling (8.21.), The extension of the procedure to benzene-1,4-diboronic acid met with limited success.29... 

Boric Oxide. Boric oxide, B203, formula wt 69.62, is the only commercially important oxide. It is also known as diboron trioxide, bone anhydride, or anhydrous boric acid. B203 is normally encountered in the vitreous state. This colodess, glassy solid has a Mohs hardness of 4 and is usually prepared by dehydration of boric acid at elevated temperatures. It is mildly hygroscopic at room temperature, and the commercially available material contains ca 1 wt % moisture as a surface layer of boric acid. The reaction with water ... 

Diboron trioxide can be used to prepare low temperature glazes because its melting point is about 600°F. 

When diboron trioxide is added to a glaze preparation having a slight amount of iron oxide, the resulting glaze may be milky or an opalescent blue. 

Allylmetal compounds can be prepared by the Pd-catalysed allylation of dimetal compounds. The phenylallylboronate 195 is prepared by the reaction of 2-phenylallyl acetate with bis(pinacolate)diboron (194) catalysed by ligandless Pd in DMSO [95], A good synthetic route to the allylsilane 197 is the reaction of Me3SiSiMe3 with geranyl trifluoroacetate (196) catalysed by ligandless Pd via transmetallation of the n-allylpalladium intermediate at room temperature in DMF [96],... 

The earliest synthesis of characterized diboron compounds was the preparation of B2C14 by Stock,1 using an electric discharge between zinc electrodes immersed in liquid BC13. Many discharge procedures have been reported for the synthesis of B2C14.21 26 Structures of some halogenated diboranes, 1, 2, and 3 are shown in Fig. 1. Diborane(6) 3 (or diboron hexahydride) has been reviewed.27 31... 

Diboron compounds, 193-250 miscellaneous reactions, 234-243 preparation, 194-206 properties of, 193... 

A method for in situ preparation of a borylcopper species from diboron and CuOAc was recently developed.200,201 The reagent coupled with allyl acetate to give allyl boronates 185 (Equation (63)).334... 

Boronic acids and boronate esters are usually prepared from lithium compounds, for example, from pyrimidines lithiated at the 5-position (Scheme 99). Boronates can also be obtained conveniently by Pd(0)-catalyzed couplings with, for example, pinacol diboron. 

A Suzuki coupling between the calixarene 1,3-diboronic acid and the 4-bromo-phenylether of tetraacetyl derivatives of corresponding glucosides, followed by deacetylation led to the derivatives 32e70 and 32f.71 The mono maltose derivative 32g was prepared in a similar way. 

Bromoboration of terminal alkynes 4 into the /J-bromo-l-alkenyl-boronic esters 5 [26], followed by a palladium-catalyzed displacement of the /J-halogen with organozinc reagents [27] is a known strategy for the preparation of metalated diene 6 (Scheme 3). An additional approach is the diboration of symmetrically disubstituted alkynes 7 with bis(pinacolato)diboron 8, followed... 

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