Deuterium reaction + cycloalkenes

Nickel has been reported to show behaviour similar to platinum [236], Further, in the reactions of cycloalkenes with deuterium, the product cycloalkanes are much more extensively exchanged over palladium than over nickel or platinum [236]. Such behaviour is not unexpected by comparison with the results obtained in the hydrogenation of linear alkenes (Sect. 3, p. 25). 

It was once thought that the exclusively cis addition was a consequence of the simultaneous addition of both hydrogen atoms. However, it has since been demonstrated that the hydrido ligands are transferred successively to the alkene and that a relatively long-lived intermediate alkyl complex is formed. The best evidence for the participation of the alkyl complex comes from hydroisomerization side reactions (equation 45), and the scrambled addition of deuterium to medium-sized cycloalkenes. ... 

To appreciate how important alkyl reversal is in the reactions being considered, the reactions of monosubstituted Ce cycles with deuterium are informative the results obtained with carbon-supported metals after 25% addition are given in Table 7.7 Remembering that deuterium numbers M of the cycloalkane greater than two mean more hydrogen exchange than cycloalkene exchange, and vice versa, the results are broadly in line with the characteristics of the three metals as exposed in the earlier sections. A certain amount of alkyl reversal must occur in all cases, but alkene desorption is only important with palladium. With Pt/C... 

Further evidence of the stereochemical constraints that determine the course of reactions of cycloalkenes with hydrogen or deuterium is obtained by studying the racemisation of (R)-(-)-10-methyl-A -octalin. The paper describing this work, and the review of G.V. Smith s contributions, " admirably summarise the... 

The B-alkyl-9-BBN undergoes an interesting reverse reaction to afford the parent alkene when treated with benzaldehyde. Consequently, the reaction is uniquely employed for the synthesis of exocyclic olefins (Chart 24.3). The hy-droboration of cyclic olefins with an internal double bond, followed by homologation with carbon monoxide in the presence of lithium trimethoxyaluminum hydride afford B-(cycloalkylmethyl)-9-BBN. This intermediate on treatment with benzaldehyde leads to an exocyclic methylene compound (Chart 24.3) [16]. Since the synthesis proceeds from the cycloalkene, thus it provides a valuable alternative to the customary methylenation of carbonyl compounds by Wittig and related procedures. The method also provides a clean synthesis of deuterium-labeled compounds (Eq. 24.10) [16], without positional scrambling or loss of label. Consequently, methylmethylene-d -cyclopentane in 52% isolated yield is obtained. 

---