Deuterium labelling addition

As another example, studies with deuterium-labeled substrates have shown that the reaction of ethanol with the coenzyme NAD+ catalyzed by yeast alcohol dehydrogenase occurs with exclusive removal of the pro-R hydrogen from ethanol and with addition only to the Re face of NAD+. 

The dominant factors reversing the conventional ds-hydroboration to the trans-hydroboration are the use of alkyne in excess of catecholborane or pinacolborane and the presence of more than 1 equiv. of EtsN. The P-hydrogen in the ris-product unexpectedly does not derive from the borane reagents because a deuterium label at the terminal carbon selectively migrates to the P-carbon (Scheme 1-5). A vinylidene complex (17) [45] generated by the oxidative addition of the terminal C-H bond to the catalyst is proposed as a key intermediate of the formal trans-hydroboration. 

A deuterium-labeling study of a reaction of this type demonstrated syn stereoselectivity in both the oxypalladation and P-elimination, which indicates that the cyclization occurs by internal migration, rather than by an anti nucleophilic capture.113 This particular system also gives products from double-bond migration that occurs by reversible Pd(II)-D addition-elimination. 

Deuterium-labelled Tetralin and deuterium were used to determine incorporation of hydrogen by structural position in the Tetralin and coal products. Approximately two-thirds of the protium incorporated into the Tetralin-di2 was found in the a-alkyl position, indicating that hydrogen exchange between the coal and tetralin involves the a-Tetralinyl radical. In the case of the coal products, the terms 2H >yFy and 1HX (1-Fy) were used to calculate the deuterium and protium contents or eacn structural position. Preferential incorporation was found in the a-aliphatic position of the soluble coal products, indicating that these positions participated preferentially in hydrogen exchange and addition. The... 

A NMR analysis of the reaction product resulting from the thermolysis of 8 in the presence of ( )-2-deuteriostyrene indicated an equal ratio of the cis and trans isomers of 2,5-dideuterio-l,l-dimethyl-3,4-diphenylgermacyclopentane. In addition, integration of the resonances for the ring protons indicated that the deuterium label was partially scrambled. It was concluded that the scrambling occurred during the cycloaddition, since... 

In light of these kinetic studies, a decrease in the concentration of the ligand is predicted to favor the a-deprotonation pathway. On the contrary, further studies show that the a/yS deprotonation ratio is independent of this concentration. This observation, associated with deuterium-labeling studies, suggests the involvement of the a-deprotonation in the formation of the ally lie alcohols at low concentration of ligand. Conversely, the presence of highly coordinating solvents such as HMPA, which break up ion pairs, suppresses both a-deprotonation and nucleophilic addition (Scheme 14) . ... 

Fig. 2.5 The fra/is-addition of dialkoxyboranes to alkynes, in the presence of triethylamine that suppresses the normal addition pathway by capturing the rhodium B-H adduct. The bold hydrogen has been traced between reactant and product by deuterium labelling. Iridium catalysts also function but less effectively.

To elucidate the reaction pathway, deuterium-labeled allenyl pinacol boronate 10 was prepared, and the addition reaction with hydrazonoester 6 was conducted in the presence of Bi(OH)3 and Cu(OH)2 (Scheme 4). In both Bi- and Cu-catalyzed cases, the reactions proceeded smoothly (in quantitative yields in both cases). In the Bi(OH)3-catalyzed reaction, a major product was allenyl compound 11, in which the internal position was deuterized. It was assumed that a propargyl bismuth was formed via transmetalation from boron to bismuth, followed by addition to hydrazonoester via y-addition to afford allenyl compound 11. Thus, two y-additions could selectively provide a-addition products [75, 76, 105, 106]. It was confirmed that isomerization of 10 did not occur. Recently, we reported Ag20-catalyzed anti-selective a-addition of a-substituted allyltributyltin with aldehydes in aqueous media [107], On the other hand, in the Cu(OH)2-catalyzed reaction, a major product was propargyl compound 12, in which the terminal position was deuterized. A possible mechanism is that Cu(OH)2 worked as a Lewis acid catalyst to activate hydrazonoester 6 and that allenyl boronate 10 [83-85] reacted with activated 6 via y-addition to afford 12. 

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