Deuteriation preferential

However, difficulties caused by isomerisation of the halo-compounds during the reaction gave rise to results which are only approximate, except for X = F. It was observed that deuteriation of the methylene group is preferred for X = Cl, while under the same conditions fluoroacetone deuteriates preferentially at the methyl group (kjkj 10). 

In contrast to that of benzyl methyl ketone, deuteriation (or dedeuteriation) of methoxyacetone occurs preferentially at the methyl group in acidic conditions (Bothner-By and Sun, 1967 Hine et al., 1967a Chevallier et al., 1969). The peculiarity of this result has been emphasised by Hine. Indeed, since the methoxy group is expected to stabilise the double bond, enol [501 must be more stable than enol [511. This conclusion is supported by the ab initio calculations of Hehre and Lathan (1972). 

H- and 19F-NMR data for both the isomers 4- and 6-fluoro-5-HTP, for 5-HTP, 4-F-melatonin, 6-F-melatonin and melatonin were obtained307. The preferential electrophilic attack of fluorine at position 4 to give 315 and 316 parallels the larger extent of deuterium exchange at position C(4) rather than at position C(6) of the deuteriated acid308. 

A particularly illuminating study involving isotopic substitution concerns the reaction of N-tritiated diethylamine with methyl benzoate (Kitamura et al., 1977). It was found that tritium was preferentially substituted into the p-position. There was also substantial substitution in the o-position but more surprising, the methyl group of the ester was labelled. It was proposed that reaction occurs as shown in Scheme 7 via radical ions [68] and [69]. 4-Cyano-benzyl-acetate, on irradiation in the presence of triethylamine is cleaved to give 4-cyanotoluene and 4,4 -dicyanobibenzyl (Ohashi et al., 1977d). When O-deuteriated methanol was used as solvent, deuterium was incorporated... 

Triphenyltin deuteride / -Deuterio- from a,j -ethylene-via a,j -dideuterio-ketones Preferential and selective deuteriation of carbon-carbon double bonds... 

Perdeuterio-3-sulfolene, K-carbonate, HgO, and dioxane stirred 48 hrs. at room temp., the solvents removed in vacuo at room temp., fresh HgO and dioxane added, again stirred 48 hrs., and this procedure repeated seven times -> 3-sul-folene-3,4-d2. Y 87%. - 3-Sulfolene-2,2,5,5-d4 can be obtained similarly by preferential deuteriation of 3-sulfolene with D2O. J. L. Charlton and R. Agagnier, Can. J. Chem. 57, 1852 (1973) ketones in pyridine s. M. A.Winnik, Synth. Commun. 5, 299 (1973). 

N-Detosylation s. a. Amines from sulfonic acid amides —, preferential 16, 367 0-Detritylation, selective 16, 3 Deuteriation 16, 694... 

---