Labeling experiment using deuterium

A similar reaction the with rran.v-isomer 3b gave c -3,5-dimethylcyclohexene (4) with very high diastereoselectivity. Accordingly, the stereochemistry of this substitution is anti. Deuterium labeling experiments using the 1-deuterio or 3-deuterio derivative of 3 a showed that the ratio of SN2 /SN2 with lithium dimethylcuprate was about 50 50, while the ratio with lithium cyano(methyl)cupratc was >96 4. 

Jun s proposed mechanism was probed by a deuterium labeling experiment using N-methyl co-catalyst 66 (Equation 9.8). Hydridoimidoyl complexes (e.g., 64), which are implicated by Jun in C—C bond formation, cannot form when secondary amine 66 is used as a cocatalyst. Instead, C—H reductive elimination from a complex... 

The mechanism has been investigated by deuterium labelling experiments using 24 and 25. ... 

A prediction of the rearrangement products a priori was not possible, because their formation depends on too many factors. Table 9 summarizes results on the reactivity of bicyclo[1.1.0]butanes . The Ni°-catalysed rearrangement of bicyclo[ 1.1.0]-butane (Table 9 entry la) proceeds via a metal-carbene complex, as was demonstrated by a deuterium-labelling experiment using 65 as a mechanistic probe (equation 33) . ... 

There are three useful mechanistic papers, the first of which is on the mechanism of electrophilic substitution, specifically mercuration, which concludes that the initial mercuration takes place on the cyclopentadienyl ring without the involvement of the metal center. The other papers, by the same author, were on the acetylation of l,l -bis(trimethylsilyl)- and l,l -bis(tributylstannyl)ferrocenes, where it was concluded through mechanistic experiments using deuterium labeling that the attack of the acetyl chloride-aluminum trichloride complex occurred at the gxo-face of the cyclopentadienyl ring followed by a proton transfer from carbon to iron. ... 

The oxidation state of the metal is of the utmost importance since no conversion is observed with complexes in a different oxidation state. CatalyticaUy active species are electron-rich d or d complexes. A general catalytic cycle has been proposed on the basis of deuterium-labeling experiments (Scheme 4-14) [280]. It is beUeved to occur for aU the catalysts used. 

The authors proposed mechanism, outlined in Scheme 9.19, was tested using a deuterium-labeling experiment. H-migration consistent with initial formation of a Pd-vinylidene was observed. The key intermediate of Buono s mechanism is a palladacyclobutane (125) resulting from [2 + 2]-cycloaddition. Direct C—C reductive elimination from intermediate 125 proceeds to give highly strained products (123), despite the apparent availability of a (l-hydride elimination pathway [39]. 

A mechanism for this reaction was tentatively proposed by the authors based on deuterium labeling experiments. The carbometallation reaction could also be performed, albeit with decreased stereoselectivity ((E)/(Z) = 1/1), using the combination of a stoichiometric amount of Zn(OTf)2 or In(OTf)3 and triethylamine, but no addition was observed for the lithium or magnesium enolates derived from 395. 

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