Cyclohexene deuterated

What concerns us here are three topics addressing the fates of bromonium ions in solution and details of the mechanism for the addition reaction. In what follows, we will discuss the x-ray structure of the world s only known stable bromonium ion, that of adamantylideneadamantane, (Ad-Ad, 1) and show that it is capable of an extremely rapid degenerate transfer of Br+ in solution to an acceptor olefin. Second, we will discuss the use of secondary a-deuterium kinetic isotope effects (DKie) in mechanistic studies of the addition of Br2 to various deuterated cyclohexenes 2,2. Finally, we will explore the possibility of whether a bromonium ion, generated in solution from the solvolysis of traAU -2-bromo-l-[(trifluoromethanesulfonyl)oxy]cyclohexane 4, can be captured by Br on the Br+ of the bromonium ion, thereby generating olefin and Br2. This process would be... 

It has been suggested previously that the thermal cycloreversion of cyclohexene to ethylene plus buta-1,3-diene proceeds via a vinylcyclobutane intermediate and that, as a consequence, the stereochemistry of deuterium labels on the cyclohexene is not reflected in the deuterated ethenes obtained. This conclusion is supported by results of a study of the stereochemistry of thermal conversion of 1 -viny 1-2.3-r/.v-didcuteriocyclo-butane to butadiene and 1,2-dideuterioethylenes equal amounts of ( )-CHD=CHD and (Z)-CHD=CHD were formed.32... 

Results for the oxidation of cyclohexene, 1,3,3-trideuterocyclo-hexene (5) and 3,3,6,6-tetradeuterocyclohexene (6) are given in Table II. It is apparent from the large increase in the relative amount of cyclohexene oxide upon deuteration of the allylic hydrogens that the hydroxylation path has a significant hydrogen-isotope effect... 

Table II. Effect of Deuteration on Cyclohexene Oxidation by Cytochrome P 450LM2...

Deuterated Cyclohexenes. 1,3,3-Trideuterocyclohexene (5) was synthesized from cyclohexanone according to the method of Fahey and Monahan (27) except that diazabicyclononane (DBN) was used instead of potassium t-butoxide in the final step. 3,3,6,6-Tetradeuterocyclohexene (6) was obtained from Merck, Sharp, and Dohme (>98%-d4). The degree of deuteration of the labeled cyclohexenes was determined by converting them to the corresponding 1,2-dibromocyclohexanes by treatment with bromine in carbon tetrachloride. The deuterium content of these dibromocyclohexanes was determined conveniently by observing the M-bromine region of the mass spectrometry. 

Lewis acid-mediated ene reaction of di- —)- / ,25)-2-phenyl-1-cyclohexyl diazenedicarboxylate with cyclohexene using tin(IV) chloride in dichloromethane at —60 °C for 5 min afforded the azo-ene adduct in 80% yield after purification by flash chromatography (eq 2). The H NMR spectrum of the azo-ene adduct recorded at 380 K in deuterated toluene established the presence of only one diastereomer. Further analysis of the ene adduct by HPLC on a Whatman Partisil 5 normal phase silica column using hexane-ethyl acetate (9 1) as eluent confirmed the presence of only one diastereomer. 

The homoallylic acetate contained all the deuteriums initially present in the deuterated cyclohexene. One of the deuteriums had been stereo-specifically transferred to an adjacent carbon. The stereochemistry of the product is most consistent with trans acetoxypalladation and cis Pd(II)-H(D) eliminations and additions (J27, 295) ... 

Steady-state, free-radical methods of LCoD generation were developed.197 The methods are versatile and work for LCo like cobalt porphyrins that are not readily reduced by borohydrides. The use of tribu-tyltin hydride has also been reported.235 The initial approach employed AIBN-cfo. Using this deuterated radical source, cis addition of the resulting LCoD was demonstrated to be the predominant mode of reaction for maleic anhydride and other cyclic olefins such as cyclohexene and 2,5-dihydrofuran. Selectivity depended upon temperature, and this important feature will be discussed below. Unfortunately, AIBN has a limited thermal operating window of 50—70 °C. Lower or higher temperatures would require the nontrivial synthesis of different deuterated azo initiators. To circumvent this problem, a second steady-state free-radical approach was developed. 

For Rh4(CO)12 as hydroformylation catalyst, several mechanistic studies including isotope labeling and kinetics have been undertaken. Thus, the deuteroformylation of 2,3,3-trimethylbut-l-ene and of styrene in the presence of Rh4(CO),2 have been studied In the first case, the 3,4,4-trimethyl-pentanal formed was found to be deuterated exclusively in the formyl position (238). In the latter case, the aldehydes formed were deuterated in the formyl and in the corresponding a-position ( > and (Zy PhCH=CHD and PhCH=CD2 were also observed (239). The mechanistic implications of these findings are not entirely clear. However, a kinetic study of the Rh4(CO)12-catalyzed low-pressure cyclohexene hydroformylation provides some evidence in favor of intact cluster catalysis A mechanism proposed on the basis of these findings includes fission of one Rh-Rh bond, whereby the tetranuclear cluster framework remains intact (Scheme 12) (240). 

A similar timing of the two steps is probably responsible for Katz and Dessau s [62] early observation that the carbonyl C atom of DPK bonds preferentially to the deuterated C atom of cyclohexene-di. 

Upon FI, four variously deuterated ethylene molecules, C2H4, C2H3D, C2H2D2 and C2HD3 are eliminated from cyclohexene-3,3,6,6-d4. 

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