Phenylethane derivatives

Table 14 Values of p for carbocation-forming dehydration" and bromination1 of l-aryl-2-phenylethane derivatives.

The VCD spectra of molecules of the form CH3C HR,R2 have been investigated in the CH stretching region (20, 57-59) and the 16(X)-900-cm mid-infrared region (59, 60). The ROA of this type of molecule has also been recorded (II-14). In particular, a-deuterated ethanol and a-phenylethane derivatives have been studied. 

In the case of a chloro, thio, or dimethylamino substituent, the hydrogen-bonded ring does not form, and the VCD due to C H stretching is weak or absent (20, 57). The characteristic methyl stretching VCD features observed for the a-phenylethane derivatives have also been interpreted in terms of currents generated about rings due to methyl-phenyl x interaction (57). 

Table 7-2. Deamination intermediates and products of 1-amino-1-phenylethane derivatives in di-oxane at 25°C after White et al. (1992 b), R = 2-naphthyl.

In non-enzymatic asym. synthesis, centre stage goes to homochiral reagents with C2-symmetry . Chiral stein (1,2-diamino-1,2-di-phenylethane) derivatives, for example, are prominent in a variety of standard transformations, although the dimethoxy-analog evidently is superior for asym. 1,4-addition to a,P-unsatd. azome-thines" . Equally valuable are axially asymmetric biaryl and binaphthyl derivs. which (like stein derivs.) may coordinate a metal template for enhancement of enantioselectivity or incorporation of... 

The asymmetric hydrosilylation that has been most extensively studied so far is the palladium-catalyzed hydrosilylation of styrene derivatives with trichlorosilane. This is mainly due to the easy manipulation of this reaction, which usually proceeds with perfect regioselectivity in giving benzylic silanes, 1-aryl-1-silylethanes. This regioselectivity is ascribed to the formation of stable 7t-benzylpalladium intermediates (Scheme 3).1,S Sa It is known that bisphosphine-palladium complexes are catalytically much less active than monophosphine-palladium complexes, and, hence, asymmetric synthesis has been attempted by use of chiral monodentate phosphine ligands. In the first report published in 1972, menthyldiphenylphosphine 4a and neomenthyldiphenylphosphine 4b have been used for the palladium-catalyzed reaction of styrene 1 with trichlorosilane. The reactions gave l-(trichlorosilyl)-l-phenylethane 2 with 34% and 22% ee, respectively (entries 1 and 2 in Table l).22 23... 

However, if positive substituents are introduced into the benzene rings, hydrazine derivatives result which considerably surpass hexa-phenylethane in their degree of dissociation. Already the colourless p-tetra-anisylhydrazine is appreciably dissociated at room temperature into the green p-dianisylnitrogen radicles (H3CO.C6H4)2N and the corre-... 

Several of this group are explosives of moderate to considerable sensitivity to impact or friction and need careful handling. Fluorodinitromethane and fluorodini-troethanol are also vesicant [ 1 ]—[4]. l-Fluoro-l,l-dinitro derivatives of ethane, butane, 2-butene and 2-phenylethane are explosive [5], Among the preparations of a series of energetic and explosive compounds, that of N, N, N, A /-tctrakis(2-fluoro-2,2-dinitroethyl)oxamide is especially hazardous, as it involves heating an undiluted explosive to a high temperature [6],... 

Not unexpectedly, alkylation of the double carbonylated complex proceeds via a base-catalysed interfacial enolization step, but it is significant that the initial double carbonylation step also involves an interfacial reaction, as it has been shown that no pyruvic acid derivatives are obtained at low stirring rates. Further evidence comes from observations of the cobalt-catalysed carbonylation of secondary benzyl halides [8], where the overall reaction is more complex than that indicated by Scheme 8.3. In addition to the expected formation of the phenylacetic and phenylpyruvic acids, the reaction with 1-bromo-l-phenylethane also produces 3-phenylpropionic acid, 2,3-diphenylbutane, ethylbenzene and styrene (Scheme 8.4). The absence of secondary carbonylation of the phenylpropionylcobalt tetracarbonyl complex is consistent with the less favourable enolization of the phenylpropionyl group, compared with the phenylacetyl group. 

Table 9.1). The rate of dehydrobromination from the intermediate bromoalkenes follows the pattern 2-bromoalkenes > Z-l-bromoalkenes > E- -bromoalkenes the corresponding chloro derivatives react more slowly. For optimum yield, the reaction temperature should be <100°C to reduce decomposition of the catalyst, and the concentration of base should be kept low to prevent isomerization of the resulting alkynes. [3-Elimination of HBr from 1,2-dibromo-1 -phenylethane can be controlled to yield 1-bromo-l-phenylethene in 83% yield [15]. The addition of alcohols and diols have a co-catalytic effect on the elimination reaction, as the alkoxide anions are transferred more effectively than the hydroxide ions into the organic phase [13]. 

The (R)-(+)-chiral 1,4-diol 17b was easily prepared from L-(+)-dimethyl tartrate. Dimethyl tartrate was converted to the corresponding phenylethylidene derivative by treatment with 1,1-dimethoxy-l-phenylethane and cat. p-toluenesulfonic acid in refluxing benzene, followed by conversion to the diol 17b with excess phenylmagnesium bromide. The diol was purified by column chromatography on silica gel (hexane ethyl acetate =5 1), and recrystalization from a mixture of hexane and 2-propanol. 

Table III shows the results of such a study. The variation in the nature of the lignin degradation products with initial pH follows the same general pattern as observed using aspen wood—i.e., an increased percentage of the phenylpropane over the phenylpropanol derivative in acid medium and the almost sole production of phenylethane products under alkaline conditions. The total yield of identified products, based on original Klason lignin, is significantly less than that for aspen (Table I).

Other 1,2-diols have also been examined. Phenylethane-l,2-diol has been oxidised using a colloid-derived Au/C catalyst (dAu = 7nm) to mandelic acid (C6HsCH(0H)C02H), an important pharmaceutical intermediate.84,85... 

Johansson and Davidsson47 have reported on the NMR studies of a mixture of two different chelating lithium amides, one with an ether chelate, derived from (R)-l-methylamino-2-methoxy-l-phenylethane (9), and one with an amine chelate (Li-4). It was found that the Et20 solution contained different dimers, both homo and hetero dimers. Based on NMR data it was concluded that a mixture of the two hetero dimers, both symmetrically ((Li-4/Li-9) 2Et20) and unsymmetrically ((Li-4/Li-9) Et20) solvated, dominated in solution. 

Reduction of T [l-(2-nitrophenyl)-l//-pyrrol-2-yl]sulfonyl -acetone or -1-phenylethan-l-one with sodium borohy-dride and 5% palladium on carbon, a reagent known to convert aromatic nitro compounds to hydroxylamines, triggers intramolecular interaction and gives pyrrolo[l,2- ][3,l,6]benzothiadiazocine derivatives 90 (Equation 11 <2001MI1405, 2004T8807>). This method was further successfully applied to the reductive cyclization of 2- [l-(2-nitrophenyl)-17/-pyrrol-2-yl]sulfanyl acetonitrile. 

Ethylbenzene or Phenylethane, C2H.5.C H5 mw 106.16 colorless liq, resembling methyl-benzene (toluene), sp gr 0.867 at 20/4°, nD 1.4959 at 20°, fr p -95-0°, bp 136.2°, fl p 85°F (29-5°C) sp heat 0.41cal/g, viscosity 0.64 centipoise at 25° heat of combstn at Cy 108.9kcal/fnole, heat of vaporization 81.1cal at bp very si sol in w (0.01% at 15°) v sol in ale, eth, benz chlf insol in Amm hydroxide. It can be prepd by heating benzene and ethylene in presence of A1 chloride with subsequent distillation, or by fractionation directly from the mixed xylene stream in petroleum refining. Purification is by rectification. It is used in org synthesis, as solvent diluent and for prepn of explosive azidonitro-, dinitro-, trinitro- higher nitrated derivatives... 

Several derivatives of mandelic add have been used as CDAs for the resolution of chiral alcohols as the corresponding esters. Thus, in a study of the steric course of the cytochrome P-450-mediated hydroxylation of phenylethane (ethylbenzene), White et al. derivatized the enzymatically formed 1-phenylethanols with (S)-O-propionylmandelyl chloride, [36], and separated the diastereomeric derivatives by GLC (153). Comber and Brouillette synthesized the enantiomers of carnitine via derivatization of a racemic precursor alcohol with (R)- or (S)-a-methoxyphenylacetic [(0)-... 

Methylene compounds with two neighboring sulfone groups can also be used for diazo transfer reactions as shown in 1964 by Klages and Bott. They obtained diazobis(ethylsulfonyl)methane (2.127) and diazobis[(diethylamino)sulfonyl)]me-thane (2.128) in aqueous ethanol and NaOH at - 5 °C and in ether with methyl-lithium at room temperature, respectively. In a similar way, methylene compounds activated by a sulfone and a carbonyl group, yield diazo derivatives, e.g., 1-diazo-l-(4 -toluene)sulfonyl propan-2-one (2.129, van Leusen et al., 1965), 2-diazo-2-(me-thylsulfonyl)-2-phenylethan-l-one (2.130, Illger et al., 1972), l-diazo-l-[(4 -nitro-phenyl)sulfonyl)]propan-2-one (2.131, Hodson et al., 1968), and other a-diazo-)ff-oxo-)ff -sulfonyl compounds (Monteiro, 1987 b) and similar diazoalkanes (van Leusen and Strating, 1988). 

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