Hydrogen-deuterium exchange alcohols

The reaction takes place extremely rapidly and if D2O is present in excess all the alcohol is con verted to ROD This hydrogen-deuterium exchange can be catalyzed by either acids or bases If D30 is the catalyst in acid solution and DO the catalyst in base wnte reasonable reaction mech anisms for the conversion of ROH to ROD under conditions of (a) acid catalysis and (b) base catalysis... 

In the presence of strong alkali, the rhodium analog of 62, or RhCl(C8H,2)PPh3, hydrogenates aliphatic ketones at 1 atm and 20°C, and after treatment with borohydride the systems similarly reduce aromatic ketones to the alcohols (526). Deuterium exchange data for acetone reduction were interpreted in terms of hydrogen transfer within a mononuclear hydroxy complex containing substrate bound in the enol form (63). 

The treatment of cyclopenta[c]thiapyrane (31a) with potassium t-butoxide in 95° O-deuterated /-butyl alcohol at room temperature resulted in more than 90"o deuteration at the 1- and 3-positions and less than 5" , at the 4-, 5-, 6-, and 7-positions.86 Thus, the hydrogen-deuterium exchange takes place at the positions calculated by quantum chemistry (see Section IV,B). Completely analogous is the same reaction in the indeno[2,l-fi]-1-benzopyrane system (44).126... 

The unconverted alcohol recovered from the reaction product was examined closely for evidence of hydrogen-deuterium exchange. Infrared... 

The phrase conducted tour mechanism was coined by Cram to describe the removal of a proton by a base and its subsequent return to a different face of the same molecule from which it was removed [Ij. Originally, the conducted tour mechanism was postulated to explain the observation that rates of racemization of deuterated carbon acids were faster than hydrogen-deuterium exchange in solutions of potassium r rr-butoxide/rerf-butyl alcohol. Thus, the basic catalyst takes hydrogen or deuterium on a conducted tour of the substrate from one face of the molecule to the [other] (ref. [1], p. 101). This process was envisioned as a rotation of the carbanion within the solvent cage. We now recognize that the secondary amine forms a mixed aggregate with the enolate, such that the reprotonation (and perhaps conformational motion) is intrasupramolecular. ... 

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