1-Arylethyl derivatives

More experimental data where the secondary KIE was larger than the EIE were subsequently published by Subramanian and Saunders (1984). The 2-arylethyl system was employed in these studies because other relevant data, such as the primary deuterium KIE, were available for this reaction. Special techniques were developed to determine the primary and the secondary tritium KIEs for this system. Three isotopically distinct elimination reactions (49-51) are possible for a 2-arylethyl derivative tracer labelled with tritium at the 2-position. 

Trifluoromethyl)copper reagents have a tendency to thermally decompose by oligomerization which is formally an a-elimination route. This pathway has been employed synthetically for the preparation of perfluoro(arylethyl) derivatives (Sections 2.1.1.3.3. and 2.1.1.3.5.). 

Metalated SAMP- or RAMP-hydrazones derived from alkyl- or arylethyl ketones 3 add to arylaldehydes both diastereo- and enantioselectively. Substituted / -hydroxy ketones with relative syn configuration of the major diastereomer are obtained with de 51-80% and 70-80% ee. However, recrystallization of the aldol adducts, followed by ozonolysis, furnishes diastereo- and enantiomerically pure (lS, S )-. yn-a-mcthyl-/3-hydroxy ketones 5 in 36-51% overall yield. The absolute configuration of the aldol adducts was established by X-ray crystallographic analysis. Starting from the SAMP- or RAMP-hydrazone either enantiomer, (S,S) or (R,R), is available using this methodology16. 

Thermal insertion occurs at room temperature when R is XCH2CHAr-, at 40° C when R is benzyl, allyl, or crotyl (in this case two isomeric peroxides are formed), but not even at 80° C when R is a simple primary alkyl group. The insertion of O2 clearly involves prior dissociation of the Co—C bond to give more reactive species. The a-arylethyl complexes are known to decompose spontaneously into CoH and styrene derivatives (see Section B,l,f). Oxygen will presumably react with the hydride or Co(I) to give the hydroperoxide complex, which then adds to the styrene. The benzyl and allyl complexes appear to undergo homolytic fission to give Co(II) and free radicals (see Section B,l,a) in this case O2 would react first with the radicals. 

Treatment of 2-arylethyl disulfides, e.g. (15), with iodine in ethylene glycol converted them to thiophene derivatives (64JOC2372). Thus (15), on heating with two equivalents of iodine in ethylene glycol, produced (17) in 60% yield. Treatment of (15) with aluminum bromide in benzene gave (16) in 40% theoretical yield, which could be oxidized by iodine... 

This gas-phase reaction provides the only method currently available for determining hydrogen-bonded pyridine free base. The method requires neither assumptions, extrapolations, nor approximations the p factor of the reaction is sufficiently small that the reactivities of the pyridine and benzene derivatives can be compared directly. The method was first introducted for determining the electrophilic reactivity of pyridine [62JCS4881 71JCS(B)2382] using 1-arylethyl acetates (9.109). Subsequent determinations used I-aryl-l-methylethyl acetates. (9.110) and i-arylethyl methyl carbonates (9.111) [79JCS(P2)228],... 

Exchange in trithiatriazepine (12.3) could also be achieved only in 5% TMSA in TFA and was likewise accompanied by decomposition. The derived rate parameters (Scheme 12.1) are again maximum values. The or-tho-aza substituent is slightly more deactivating than the ortho nitro, and closely similar effects were predicted earlier from data on pyrolysis of 1-arylethyl acetates [62JCS4881 71JCS(B)622],... 

I, 4,7,10-Tetraazacyclododecane Derivatives Obtained Therefrom and N-Arylethyl-ethanolamine Sulfonate Esters as Intermediates... 

The gas-phase stability of the ethylenephenonium ion [25C ] and its ring-substituted derivatives has also been determined by the bromide-transfer equilibria (31) of jS-arylethyl bromides (Mishima et al., 1990c). 

Styrenes are available by dehydration of either a-arylethyl or /S-aryl-ethyl alcohols. The procedures were reviewed in 1S>49. /S-Phenylethyl alcohol loses water at 140° over a roixture of molten sodium and potassium hydroxides to give styrene, C,H5CH=CH2, in 57% yield. The 2,4-dimethyI derivative has been prepared in a similar manner from the primary alcohol. " Many substituted styrenes have been made by dehydration of methylarylcarbinols with potassium hydrogen sulfate, phosphorus pentoxide, or activated alumina. 1,1-Diphenyl-ethylene and 2-phenyl-2-butene are easily obtained by boiling the corresponding tertiary alcohols with dilute sulfuric acid. 

The appearance of a double bond in the 9 10 position during the formation of a-codeimethine was consistent with the attachment of the basic nitrogen to one of these carbon atoms. Position 9 was generally preferred by the early theorists, probably on conscious or subconscious biogenetic grounds, in that the other opium alkaloids are /3-arylethyl-amine derivatives. 

Hydrogenolysis of several substituted 2-, 4-, and 5-aminooxazole derivatives has been studied by Tanaka and his co-workers,373-376 Thus, hydrogenation of benzyl 5-aryloxazole-2-carbamates (221) or of 2-amino-5-aryloxazoles (222) over palladium-carbon in ethanol or platinum oxide in acetic acid gives l-(2 -arylethyl)ureas.373 374... 

Antifungal activity of pyrano- and furanocoumarins (natural and synthetic) has been studied and reported by different authors. For example, 4-arylethenyl and 4-arylethyl-6,7-dihydropyranocoumarin derivatives (70-79) have been reported to show in vitro antifungal activity against niger [72 (48.6%), 73 (55.3%), 74 (54.7%)], and A. flavus [74 (58.1%), 75 (49.9%)] in comparison with the reference compound Bavistin (80.0%) [266]. 

Bis(arylethyl)phosphine sulfides were added to the triple bond of acetylenic derivatives in the presence of potassium hydroxide in DMSO leading to the formation of double thiophosphinylated products (Scheme 26). ... 

---