Efficient Hydrogenation of Sterically Hindered Olefins with Borane−Methyl Sulfide Complex

Abstract

Sterically hindered olefins are efficiently reduced to the corresponding alkanes by the borane−methyl sulfide (BMS) complex at room temperature (or below) in dichloromethane containing a mild one-electron oxidant (such as an aromatic cation radical) or by the passage of an anodic current. In an alternative procedure, the hydrogenation of the same (electron-rich) olefins with the BMS complex (in the absence of a one-electron oxidant) is also carried out in the presence of a strong Brønsted acid (such as HBF4). In the oxidative activation, olefin cation radicals are the first observable intermediates, and separate experiments (including transient electrochemistry) confirm the facile reduction of the olefin cation radical by borane to produce the corresponding alkane. The direct protonation of olefins produces carbocationic intermediates which are also efficiently reduced by borane to the corresponding alkanes. The intermediacy of both olefin cation radicals and carbocations in the hydrogenation procedure with borane is discussed.

Synthesis and Heck Reactions of Ethenyl- and (Z)-Butadien-1-yl Nonaflate Obtained by the Fragmentation of Furan Derivatives

“…[30] (Z)-1-trimethylsiloxybuta-1,3-diene (7) [31] and 4-tertbutyl-1-(trimethylsiloxy)cyclohexene were prepared according to literature procedures (ref. [10,32] respectively). TLC analysis was performed on Merck silica gel 60 F 254 plates.…”

Disproportionation and Structural Changes of Tetraarylethylene Donors upon Successive Oxidation to Cation Radicals and to Dications

“…The olefinic and aromatic electron donors 1,1,2,2-tetrakis(4-methoxyphenyl)ethylene ( 1 ),3c 1,1,2,2-tetrakis(4-methylphenyl)ethylene ( 2 ),1d 3,4-bis(4-methoxy-phenyl)-hex-3-ene ( 4 ), 2,3-bis(4-methoxyphenyl)bicyclo-[2.2.2]oct-2-ene ( 5 ), 4,4‘-dimethoxybenzhydrylidene-adamantane ( 6 ),1d octamethylbiphenylene ( 7 ), and tetrakis(bicyclo[2.2.2]octano)cyclooctatetraene ( 8 ) 24 have been described previously. The McMurry coupling of 4-methoxy-4‘-methylbenzophenone with titanium tetrachloride and zinc dust in tetrahydrofuran afforded 1,2-bis(4-methylphenyl)-1,2-bis(4-methoxyphenyl)ethylene ( 3 ) in 91% yield.…”

Switching the Photochromic Activity of Acenaphthylene Derivatives through a Tandem Nucleophile‐Promoted Addition Reaction

“…However, in our hands, these conditions afforded ketones 11 and 12 as the only products. Therefore, we decided to split the transposition and reduction steps, employing HCl in AcOH to promote both the rearrangements and LiAlH 4 to reduce the ketone. These reactions are fast and clean and afforded the alkenes 15 and 16 in excellent overall yield without the need to isolate the intermediates.…”