Ionic hydrogenated

Ayotte P, Bailey C G, Weddle G FI and Johnson M A 1998 Vibrational spectroscopy of small Br (Fl20) and I Fl20) clusters infrared characterization of the ionic hydrogen bond J. Phys. Chem. A 102 3067-71... 

Meot-Ner M 1984 Ionic hydrogen bond and ion solvation 2. Solvation of onium ions by 1-7 water molecules. Relations between monomolecular, specific and bulk hydration J. Am. Chem. Soc. 106 1265-72... 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

The hybridic nature of the Si—H bond is utili2ed to generate C—H bonds by ionic hydrogenation according to the foUowiag general mechanism, ia which a hydride is transferred to a carbocation. 

KURSANOV PARNES Ionic Hydrogenation A non-calalytK hydrogenation of C C. C O, C N bonds and hydrogenotysis of C-OH, C Hal etc, under the action of an acid and a hydride ion donor... 

A considerable extension of the synthetic utility of the hypoiodite reaction is achieved if the steroid hypoiodite (2) is generated from the alcohol and acetyl hypoiodite and then decomposed in a nonpolar solvent. In this case ionic hydrogen iodide elimination in the 1,5-iodohydrin intermediate (3) is slow, thereby allowing (3) to be converted into an iodo hypoiodite (5). 

The rutro groups of a- or fi-nitrosulfides are cleanly replaced by hydrogen via ionic hydrogenation to give sulfides, as shown in Eqs 7 93-7 95 The attack of hydnde takes place at the mote subsdnited carbon... 

Iododesilylation, 41 of aryltrimethylsilanes, 42 Iodomethyltrimethylsilane, 27 4-Iodophenylalanine, 42 Ionic hydrogenation, 136 Ireland-Claisen rearrangement, 112-14 ftwtf-2 Isocyanocyclohexanol, 137 Isophorone, 52 Isophorone dienol ether, 135 (Isopropoxydimethylsilyl)methyl magnesium chloride, 58... 

D. N. Kursanow, Z. N. Parnf.s u. N. M. Loim, Applications of Ionic Hydrogenation to Organic Syntheses, Synthesis 1974, 633. 

Benzylic or allylic oxygen functions react with Lewis acids such as trifluoroacetic acid to generate allyl or benzylic cations which abstract a hydride from silanes such as triethylsilane 84 b to result in the removal of the oxygen function in a process which has been called ionic hydrogenation and which has been reviewed [34-38]. 

Limited studies of the germanium and tin hydride analogs of the silicon hydrides show that they share this ability to function as hydride sources in ionic hydrogenations however, their relatively greater reactivity toward acids appears to restrict their practical applications in organic synthesis.24,25... 

The conversion of alcohols directly into the structurally related hydrocarbons by ionic hydrogenation can provide a means of synthesis for compounds that would be extremely difficult or impossible to obtain by other methods. A good example is the synthesis of 2-terr-butyladamantane (12, R = Me). This interesting, highly strained compound may be synthesized in moderate overall yield by a conventional multiple-step route.149 Alternatively, it is obtained in 90% isolated yield upon treatment of a dichloromethane solution of the readily available 2-/c/7-bulyI -2-adamantanoI (11, R = Me)150 and one equivalent of either tri-n-hexylsilane151152 or triethylsilane153 with trifluoroacetic acid at room temperature (Eq. 16). 

Alkenes to Alkanes. The ionic hydrogenation of many compounds containing carbon-carbon double bonds is effected with the aid of strong acids and organosilicon hydrides following the n-route outlined in Eq. 2. A number of factors are important to the successful application of this method. These include the degree and type of substituents located around the double bond as well as the nature and concentrations of the acid and the organosilicon hydride and the reaction conditions that are employed. 

The use of deuterated organosilicon hydrides in conjunction with proton acids permits the synthesis of site-specific deuterium-labeled compounds.59 126 221 Under such conditions, the deuterium atom in the final product is located at the charge center of the ultimate carbocation intermediate (Eq. 62). With the proper choice of a deuterated acid and organosilicon hydride, it may be possible to use ionic hydrogenation in a versatile manner to give products with a single deuterium at either carbon of the original double bond, or with deuterium atoms at both carbon centers.127... 

The behavior of the isomeric dihydronaphthalenes emphasizes the importance of the relative stabilities of carbocation intermediates in ionic hydrogenations. Treatment of 1,2-dihydronaphthalene with Et3SiH/TFA at 50-60° gives a 90% yield of tetralin after one hour. Under the same conditions, the 1,4-dihydronaphthalene isomer gives less than 5% of tetralin after 70 hours.224 This difference in reactivity is clearly related to the relatively accessible benzylic cation formed upon protonation of the 1,2-isomer compared to the less stable secondary cation formed from the 1,4-isomer.224... 

Trisubstituted Alkenes. With very few exceptions, trisubstituted alkenes that are exposed to Brpnsted acids and organosilicon hydrides rapidly undergo ionic hydrogenations to give reduced products in high yields. This is best illustrated by the broad variety of reaction conditions under which the benchmark compound 1-methylcyclohexene is reduced to methylcyclohexane.134 146,192 202 203 207-210 214 234 When 1-methylcyclohexene is reduced with one equivalent of deuterated triethylsilane and two equivalents of trifluoroacetic acid at 50°, methylcyclohexane-... 

Exceptions to the generally facile ionic hydrogenation of trisubstituted alkenes include the resistance of both 2-methyl-1-nitropropene (R = NO2) and 3,3-dimeth-ylacrylic acid (R = CO2H) to the action of a mixture of triethylsilane and excess trifluoroacetic acid at 50° (Eq. 85).234 The failure to undergo reduction is clearly related to the unfavorable effects caused by the electron-withdrawing substituents on the energies of the required carbocation intermediates. 

Tetrasubstituted Alkenes. Tetrasubstituted alkenes lacking electron-withdrawing substituents undergo facile ionic hydrogenation to alkanes in very good yields. Simple examples include 2,3-dimethyl-2-butene,208,214 1,2-dimethyl-cyclopentene, 1,2-dimethylcyclohexene,229 and A9(10)-octalin.126,204,212... 

Interesting variations are observed in the stereoselectivities of these ionic hydrogenations. Reduction of 1,2-dimethylcyclopentene with Et3SiH/TFA near... 

Polyenes. The behavior of substrates with multiple carbon-carbon double bonds toward the conditions employed for ionic hydrogenations with organosilicon hydrides depends heavily on the number and kinds of substituents and... 

Reduction of dienes incorporated into steroid structures may lead to different configurations in the products. For example, treatment of 8(9),14(15)-bisdehydroestrone 42 (R = H) for four hours at room temperature with twenty equivalents of trifluoroacetic acid and two equivalents of triethylsilane leads to an ionic hydrogenation product mixture containing the natural 8/1,9a,14a-estrone 43 as a minor component (11%) and the 8a,9/i, l 4/i-isomcr 44 as the major component (83%) (Eq. 92).241 The related methyl ether (42, R = Me) behaves in a similar fashion.241 The yield of natural isomer 46 formed from the methyl ether of A8(9),i4(i5)-bigdehydroestradiol analog 45 increases from 22 to 34%, and that of... 

Homoconjugation results in enhanced reactivity of substrates toward ionic hydrogenation. Bicyclo[2.2.1]hepta-2,5-diene forms a mixture of the trifluoroac-etate esters of bicyclo[2.2.1]hepten-2-ol, tricyclo[2.2.1.02 6]heptan-3-ol, and bicyclo[2.2.1]heptan-2-ol in a 62 20 17 ratio on treatment with 10 equivalents of triethylsilane and 20 equivalents of trifluoroacetic acid for 24 hours at room temperature (Eq. 96), 230... 

Based on the few reported examples, the pattern of ring cleavage that accompanies the ionic hydrogenation of alkylidenencyclopropanes seems to be related to the pattern and degree of substitution on both the ring and the double bond.233 Thus, treatment of l,l-dimethyl-2-methylenecyclopropane with two equivalents of triethylsilane and four equivalents of trifluoroacetic acid for 90 hours at room temperature yields 65% of 2,3-dimethylbutane (Eq. 114).229 Exposure of 1,1-dimethyl-2-isopropylidenecyclopropane to the same ratio of reactants at 50° for 16 hours produces a complex mixture containing 63% of 2,5-dimethylhexane, 18.5% of 2,5-dimethyl-3-hexene, 1.6% of 2,5-dimethyl-2-hexene, and 7% of 2,5-dimethyl-2-hexyl trifluoroacetate (Eq. 115).229... 

Kursanov, D. N. Parnes, Z. N. Kalinkin, M. I. Loim, N. M. Ionic Hydrogenation and Related Reactions-, Harwood Academic Publishers Chur, Switzerland, 1985. 

Iodoalkane, oxirane iodoreduction to, cyclohexyl iodide, 136 4-Iodobenzyloxytriethylsilane, ether reduction, 126 Ionic hydrogenation ... 

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