Boronate cyclic aryl

A simple preparation of cyclic vinyl boronates has been achieved from vinyl triflates of N-protected tetrahydropyridines. Suzuki coupling of the boronates with aryl bromides, iodides, and triflates proceeds in good yield to give 4-aryl tetrahydropyridines (Eq. (73)) [116]. 

Boronic acids readily dehydrate at moderate temperatures (or over P4O10 at room temperature) to give trimeric cyclic anhydrides known as trialkyl(aryl)boroxines ... 

The optimal reaction conditions were applied with 59d in the addition of various aryl boronic acids and potassium trifluoroborates to several cyclic and acyclic enones (Fig. 8). Arylboronic acids added to cyclic enones in high yields (89-97%) and with good to excellent selectivities (85-98% ee). Under these conditions, the potassium trifluoroborate reagents reacted at faster rates, but with slightly lower selectivities (83-96% ee). The reactions of acyclic enones with aryl boron reagents gave also excellent yields (83-96%). 

Boron trifluoride etherate was used in conjunction with the reducing agent borane to rearrange aromatic O-triisopropylsilyl ketoximes to cyclic and acyclic aniline derivatives. The steric hindrance of the substituents on the silicon atom, the size of the aliphatic ring and the presence of alkoxy substituents on the aryl group played important roles in the aniline formation. 

Cyclotriboroxanes (RBO)3 (also known as boroxines) are formally anhydrides of the corresponding boronic acids RB(OH)2 only mild heating is required to convert these dibasic acids into a wide range of cyclic trimeric anhydrides [eqn (9.18)]. This dehydration process can be adapted for the synthesis of B3O3 rings with different aryl groups on the boron atoms by using two or more arylboronic acids in the appropriate stoichiometric ratio. 

The general formula for boric acid esters is B(OR)3. The lower molecular weight esters such as methyl, ethyl, and phenyl are most commonly referred to as methyl borate [121 -43-7], ethyl borate [150-46-9], and phenyl borate [1095-03-0], respectively. Some of the most common boric acid esters used in industrial applications are Us ted in Table 1. The nomenclature in the boric acid ester series can be confusing. The IUPAC committee on boron chemistry has suggested using thalkoxy- and triaryloxyboranes (5) for compounds usually referred to as boric acid esters, trialkyl (or aryl) borates, trialkyl (or aryl) orthoborates, alkyl (or aryl) borates, alkyl (or aryl) orthoborates, and in the older literature as boron alkoxides and aryloxides. Cyclic boric acid esters, which are trimeric derivatives of metaboric acid (HB02), are known as boroxines (1). 

Cyano compounds liquid crystals, 12, 278 in silver(III) complexes, 2, 241 Cyanocuprates, with copper, 2, 186 Cyano derivatives, a-arylation, 1, 361 Cyanosilanes, applications, 9, 322 Cyclic acetals, and Grignard reagent reactivity, 9, 53 Cyclic alkenes, asymmetric hydrosilylation, 10, 830 Cyclic alkynes, strained, with platinum, 8, 644 Cyclic allyl boronates, preparation, 9, 196 Cyclic allylic esters, alkylation, 11, 91 Cyclic amides, ring-opening polymerization, via lanthanide catalysis, 4, 145... 

Hoffmann et al have reported the addition of allyl(dimethoxy)borane to linear and branched a-aryl-aldimines (entries 16-19, Table 2). The absence of a-deprotonation may be explained by a delicate balance between the basicity and the reactivity of the allylboronate. Allyl(dimethoxy)borane should thus be considered the reagent of choice in reactions with enolizable aldimines. Reactions are conveniently carried out at 25 °C in CH2CI2 and work-up is performed using triethanolamine to break up amine-boronate complexes. Allyl(dimethoxy)borane also adds to the cyclic imine, A -piperideine, in 90% yield. The reported yields for the addition of allyllithium and allylmagnesium chloride to A -piperideine are low. 

The addition of allylboronates (105) and (106) to aryl sulfenimines (104) to provide sulfenamides (107) has also been reported by Wuts and Jung (equation 23). High yields of (107) are obtained even though the reaction is slow (4 h to 3 d, refluxing toluene). The reaction rate is a function of the size of the boronate ligand (106 is slower than 105). The authors attribute the reaction sluggishness to a cyclic boro-nate transition state. 

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. 

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