D. G. Pershin

Regioselective β‐Hydride Transfer in Reactions of Ate Complexes of Boron Bicyclic and Cage Compounds. Synthesis of Methylenecyclohexane Derivatives.

Abstract The reactions of bicyclic and cage boron containing ate complexes with AcCl have been studied, the key stage of which involves β-bridgehead hydride abstraction. The ate complexes of 7-substituted 3-methyl-3-borabicyclo[3.3.1]non-6-ene were converted to the corresponding 5-methylene-3-alkylcyclohex-2(3)-en-1-ylmethyl(dialkyl)boranes 14 and 15 . A synthetic application of the reaction is illustrated by conversion of compounds 14 and 15 to 3,5-dimethylene-1-R-cyclohexenes 16 , particularly to 3,5-dimethylene-1-isopropenylcyclohexene ( 16c ) The β-hydride transfer in ate complexes of 2-alkyl-1-boraadamantane and of 4-alkyl-3-borahomoadamantane occurs regioselectively, at the unsubstituted bridgehead, to give, respectively, 2-alkyl-7-methylene-3-borabicyclo[3.3.1]nonanes and 8-methylene-3- borabicyclo[4.3.1]decanes.

A novel method of synthesis of 1-azaadamantane from 1-boraadamantane

Abstract A novel and convenient method for the synthesis of 1-azaadamantane (I) from the 1-boraadamantane-tetrahydrofuran complex (XIII) is described. This is based on an intramolecular reaction of organic azides with organoboron compounds. Treatment of the boron cage compound XIII with iodine and an excess of sodium azide followed by oxidation (H 2 O 2 , OH − ) affords 7α-hydroxymethyl-3-azabicyclo[3.3.1]nonane (VII), cyclization of which leads to I in 40% overall yield. Some new boron cage compounds were also isolated, diazidoborane (XIV) being of particular interest.

COMPLEXES OF 1-BORAADAMANTANE AND ITS DERIVATIVES WITH 1-AZAADAMANTANES : SYNTHESIS AND MOLECULAR STRUCTURE

The reactions of 1-boraadamantane and 2-methyl-, 2-ethyl-, 2,2-dimethyl-, and 3,5-dimethyl-substituted 1-boraadamantanes with their 1-azaadamantane analogs afforded a series of 1:1 adducts, which are stable to atmospheric air and moisture.IH,13C, and31B NMR spectra as well as mass spectra of the compounds synthesized were investigated. Only the adduct of 2,2-dimethyl-1-boraadamantane with 2,2-dimethyl-1-azaadamantane readily dissociates into the initial components due to steric hindrances that prevent strong B→N coordination. The structure and geometric parameters of the 1-boraadamantane complex with 3,5-dimethyl 1-azaadamantane were established by X-ray diffraction analysis.

2-Phenyl-1-boraadamantane complexes. Crystal structure and use in the synthesis of cage compounds

Complexes of 2-phenyl-1-boraadamantane with trimethylamine and pyridine were studied by X-ray diffraction analysis. The 2-phenyl-1-boraadamantane adduct with tetrahydrofuran (1) was transformed to 1-hydroxy-2-phenyladamantane via a carbonylation—oxidation sequence. The intramolecular version of the organoborane reaction with organic azides was employed as a key step in the transformation of 2-phenyl-1-boraadamantane adduct (1) into 2-phenyl-1-azaadamantane (5).

2-Phenyl-1-boraadamantane complexes. Synthesis and intramolecular dynamics

The reaction of triallylborane with 3-phenylprop-1-yne at 135–140 °C followed by treatment of the reaction mixture with MeOH afforded 7-benzyl-3-methoxy-3-borabicyclo[3.3.1]non-6-ene (1) in 81% yield. Hydroboration of compound1 with a solution of BH3 in THF yielded the tetrahydrofuran complex of 2-phenyl-1-boraadamantane (2). The reactions of trimethylamine or pyridine with compound2 afforded the trimethylamine (3) or pyridine (4) complexes of 2-phenyl-1-boraadamantane. respectively. Hindered rotation about the C(2)−Ph bond in adduct3 was observed by1H and13C NMR spectroscopy. The activation energy of this process is 58.6 kJ mol−1 (determined by 2D1H−1H EXSY spectroscopy).

Synthesis of 1,2-bis(1-boraadamant-2-yl)ethane derivatives. Crystal structure of the racemic form

Condensation of triallylborane with octa-1,7-diyne followed by treatment of the reaction mixture with methanol afforded a mixture of stereoisomeric 1,4-bis(3-methoxy-3-bora-bicyclo[3.3.1]non-6-en-7-yl)butanes (1a,b). Hydroboration of the latter with a solution of BH3 in THF yielded the tetrahydrofuran complex of 1,2-bis(1-boraadamant-2-yl)ethane (2) as a mixture of diastereomers. Pure racemate (2a) was obtained by crystallization from the reaction mixture and it was converted into the pyridine complex of 1,2-bis(1-boraadamant-2-yl)ethane (3). The structure of the latter was established by X-ray diffraction analysis. Complex2a was converted into the corresponding racemic 1,2-bis(1-hydroxyadamant-2-yl)ethane (4a) by the carbonylation-oxidation reaction.