P-methylphenylboronic acid

To demonstrate the applicability of this support in organic synthesis, the authors immobilized a (p-bromophenyl) acetic acid which was then transformed into the corresponding biaryl by means of the Suzuki cross-coupling reaction with p-methylphenylboronic acid. Quantitative NaOH cleavage of the ester linkage yielded the released biaryl, of which no purity was mentioned. 

Keywords iodobenzene, p-methylphenylboronic acid, Suzuki coupling, KF/ AI2O3, palladium powder, microwave irradiation, 4-methylbiphenyl... 

To a mixture of KF/A1203 (0.950 g, 40% by weight) and palladium black (0.050 g, 0.470 mmol, 99.9+% as a submicron powder) contained in a clean, dry, round-bottomed flask was added p-methylphenylboronic acid 2 (0.150 g, 1.10 mmol). The solid mixture was stirred at room temperature in the open air... 

Various arylboronic acids having o-, m-, and p-substituents smoothly underwent the addition to benzyl crotonate (7e) with high yields and high %ee (entries 5-11). There is no appreciable difference in yields and %ee between m- and p-functionalized arylboronic acids. The presence of o-substituent slightly retarded the addition due to its steric hindrance (entries 10 and 11) and the methoxy group again diminished the %ee (entry 11). The addition of 4-methylphenylboronic acid and 1-naphthylboronic acid to 7g resulted in 48 and 1 l%ee, respectively (entries 12 and 13). 

To a dichloromethane solution (5 ml) containing triphenylbismuth difluoride (239 mg, 0.50 mmol) and 4-methylphenylboronic acid (68 mg, 0.50 mmol) was added boron trifluoride diethyl etherate (65 p.1, 0.50 mmol) at 0°C, and the resulting mixture was stirred at room temperature for 2 h. An aqueous solution (20 M) of sodium fluoroborate (500 mg, 4.55 mmol) was then added and the two-phase mixture was vigorously stirred for 30 min. The water phase was extracted with dichloromethane (5 ml X 2), and the combined extracts were dried over MgS04, and passed through a short silica gel column. Evaporation of the solvent under reduced pressure left an oily residue, which was crystallized from ether-dichloromethane (10 1) to yield (4-methylphenyl)triphenylbismuthonium tetrafluoroborate (300 mg, 97%) as a colorless solid [980M4332]. 

These ICT sensors have one drawback for potential real-world sensor development, which is pH sensitivity. In the case of fluorescent photo-induced electron transfer (PET) sensors, the interaction between o-methylphenylboronic acids (Lewis acids) and proximal tertiary amines (Lewis bases) has been exploited, while the precise nature of the amino base-boronic acid (N- B) interaction is deba-jgjj 8,9,27,29 jjjg interaction between a boronic acid and proximal amine lowers the p Ta of the boronic and allows pH-insensitive binding over a wide range. 

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