Isotopic labeling decarbonylation

Photochemical decarbonylation of C i9)-aldehydes (e.g. 34) occurs with intramolecular transfer of the aldehydic hydrogen to C(io> (35) [38,39,40], as revealed by isotopic labelling. The... 

Watanabe reported that the addition of C-H bonds in aldehydes to olefins takes place efficiently ivith the aid of Ru3(CO)i2 under a CO atmosphere at 200 °C (Eq. 9.44) [62]. In the case of the reaction with 1-hexene, a mixture of linear and branched ketones was obtained in 35% and 12% yields, respectively. The use of a CO atmosphere is the key to accomplishing this reaction in a catalytic manner. These authors revealed the role of CO by means of isotope-labeling experiments using CO. The presence of CO is essential for suppressing the decarbonylation of aldehydes and for stabilizing the active catalyst species. Interestingly, the reaction using 1,3-dienes as an acceptor of the C-H bond proceeds in the absence of CO (Eq. 9.45) [63]. Aromatic and heteroaromatic aldehydes can also be used in this reaction. 

Let us consider the photolysis of DBK on NaX as a standard system (Table 3). Under a vacuum or in an argon atmosphere, the major product is 1,2-diphenyl ethane (DPE) which results from diffusional separation of the primary radical pair, followed by decarbonylation and random coupling of the benzyl radicals produced in the secondary radical pair. These results, along with isotopic labelling experiments, show that diffusional motion of primary and secondary radical pairs is fast compared to coupling or decarbonylation reactions of the primary or the secondary radical pairs. The results for... 

The decarbonylation of the two isotopically labeled pentenals shown below have been studied. Explain why the distribution of deuterium found in the products is affected by solution concentration. 

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