Boron-11 NMR spectroscopy

The determination of the location of the deuterium atoms in these two compounds was accomplished by the use of infra-red 149> and boron-11 nmr spectroscopy. These techniques also showed that complete scrambling occurred in about 1.3 hours at room temperature and the... 

Boron-11 NMR spectroscopy can be used for structural elucidation of complex boron containing heterocycles. Hydrolytic stabilities of dioxazabora heterocycles (19) and their corresponding N Mannich bases with different carboxamides have been determined by nB NMR studies (82M1025). 

A number of 5,5-dialkyldihydro-4.ff-l,2,3-triazole-4-ones and 5-amino-4,4-diphenyl-4//-1,2,3-triazoles have been studied by N NMR spectroscopy. Their N chemical shifts (corrected to the external standard of ammonia) are listed in Figure 11 <93CB103>. The N NMR spectra of triazole and benzotriazole boron derivatives have been reported <89IC4022>. 4-(l-Azido-l-methylethyl)-lH-1,2,3-triazole shows N chemical shifts (D20/pyridine, MeN02 external standard) 3 — 284.6 (Na), - 161.5 (Ny), d - 135.8 (N/9), d-9lA,d- 79.2, and d - 60.4 ppm <89CB9l 1>. 

Cyclization of enone (9) in hexane with boron trifluorideetherate in presence of 1,2-ethanedithiol, followed by hydrolysis with mercury (II) chloride in acetonitrile, yielded the cis-isomer (10) (16%) and transisomer (11) (28%). Reduction of (10) with lithium aluminium hydride in tetrahydrofuran followed by acetylation with acetic anhydride and pyridine gave two epimeric acetates (12) (32%) and (13) (52%) whose configuration was determined by NMR spectroscopy. Oxidation of (12) with Jones reagent afforded ketone (14) which was converted to the a, 3-unsaturated ketone (15) by bromination with pyridinium tribromide in dichloromethane followed by dehydrobromination with lithium carbonate and lithium bromide in dimethylformamide. Ketone (15), on catalytic hydrogenation with Pd-C in the presence of perchloric acid, produced compound (16) (72%) and (14) (17%). The compound (16) was converted to alcohol (17) by reduction with lithium aluminium hydride. 

In order to allow for a closer approach of the boron centers, the introduction of flat cyclic boryl moieties with reduced steric hindrance has also been pursued. Thus, the reaction of 26 with 9-chloro-9-borafluorene and 5-bromo-10,11 -di-hydrodibenzo[b,f]borepin resulted in the formation of diboranes 31 and 32 which bear two different boryl moieties at the pen-positions of naphthalene (Scheme 13).34 These diboranes have been characterized by multinuclear NMR spectroscopy and X-ray single-crystal analysis. In 31, the boron center of the borafluorenyl moiety is -coordinated by the zpso-carbon of a mesityl group with which it forms a contact of 2.730(3) A (Fig. 8). As a result of this interaction, the boron center involved in this contact is slightly pyramidalized (Xangie = 355.7°). In the case of 32 (Fig. 9), the distance between the boron center of the boracylic moiety and the ipso-carbon of... 

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