Ionic hydrogenations using boron trifluoride hydrate. Reductions of polycyclic aromatics

Ionic and Organometallic‐Catalyzed Organosilane Reductions

“…207 Acids that are used in addition to trifluoroacetic acid include trifluoroacetic acid with added sulfuric acid 203 or boron trifluoride etherate, 210,211 perfluorobutyric acid, 212 hydrogen chloride/aluminum chloride, 136,146,213 perchloric acid in chloroform, 214 p-toluenesulfonic acid alone 134 or with aluminum bromide or aluminum chloride, 192 concentrated sulfuric acid in two-phase systems with dichloromethane, alcohol, or ether solvents, 209,215 trifluoromethanesulfonic acid, 216 chlorodifluoroacetic acid, 134 and the monohydrate of boron trifluoride (BF 3 •OH 2 ). 217 The use of a sulfonated phenol-formaldehyde polymer in conjunction with formic acid is also reported. 208 Acids that are ineffective include phosphoric, 208 trichloroacetic, dichloroacetic, and acetic acids.…”

“…Use of boron trifluoride hydrate (BF 3 •OH 2 ) as the acid in conjunction with triethylsilane causes the reduction of certain activated aromatic systems. 217,262 Thus, treatment of anthracene with a 4-6 molar excess of BF 3 •OH 2 and a 30% molar excess of triethylsilane gives 9,10-dihydroanthracene in 89% yield after 1 hour at room temperature (Eq. 120).…”

“…Naphthalene, phenanthrene, 1-methylnaphthalene, 2-naphthalenethiol, phenol, anisole, toluene, and benzene all resist reduction under these conditions. 217 Use of deuterated triethylsilane to reduce 1-methoxynaphthalene gives tetralin-1,1,3-d 3 as product, thus yielding information on the mechanism of these reductions. 262 2-Mercaptonaphthalenes are reduced to 2,3,4,5-tetrahydronaphthalenes in poor to modest yields.…”

“…262 2-Mercaptonaphthalenes are reduced to 2,3,4,5-tetrahydronaphthalenes in poor to modest yields. 217 The combination of PhMeSiH 2 (or Ph 2 SiH 2 ) and Cp 2 TiMe 2 (10 mol%) reduces pyridines to N-silylated-di-or tetrahydropyridines or the N-silylated piperidines. 264,265 With quinoline, only the pyridine ring is reduced preferentially to the benzene ring (Eq.…”

“…A number of reagents have been employed in the direct reduction of aromatic ketones such as acetophenone to the corresponding methylene derivatives. These include Et 3 SiH/BF 3 •OEt 2 , 210,217,375,413 Et 3 SiH/TFA, 73,135,180,207,210,257,376,414 -419 135 and Et 3 SiH (or PhMe 2 SiH)/TiCl 4 . 421 Diaryl ketones are reduced with Et 3 SiH/PPHF (pyridinium poly(hydrogen fluoride)) in excellent yields.…”