ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Reduction of (+)-[3,3-2H2]camphor ([3,3-2H2]1) with lithium, sodium or potassium in ammonia and a co-solvent gave; 1) the enolate of [3,3-2H2]1 and the alcoholates of (-)-[2,3,3-2H3]isoborneol ([2,3,3-2H3] and (+)-[2,3,3-2H3]borneol ([2,3,3-2H3]3); 2) the alcoholates of [3,3-2H2]2 and [3,3-2H2]3; 3) the dialcoholates of the pinacols [3,3,3′,3′-2H4]4 and [3,3,3′,3′-2H4]5. It is proposed that these are formed from the ketyls [3,3-2H2]1- M+, by: 1) disproportionation; 2) H-atom abstraction from the medium; 3) dimerization. Protonation upon work-up afforded [endo-32H]1, [2,3,3-2H3]2, [2,3,3-2H3]3,[3,3-2H2]2, [3,3-2H2]3, [3,3,3′,3′-2H4]4 and [3,3,3′,3′-2H4]5. Pinacol [3,3,3′,3′-2H4]5 was the main and pinacol [3,3,3′,3′-2H4]4 a minor product in the reductions with lithium and both were minor products in the reductions with sodium; pinacols were not formed in the reductions with potassium. Parallel reductions of 1, unlabeled, analogously led to 2, 3, 4 and 5, and the ratios 2/3 differed from the ratios ([2,3,3-2H3]2+[3,3-2H2] 2/([2,3,3-2H3]+[3,3-2H2]3) under certain conditions. Different values for these ratios were found in the reductions with each metal, all of which corresponded to low overall diastereoselectivities. Reactions 1 and 3 persisted when the reductions were carried out in ammonia/water/co-solvent mixtures and the enolate formed via reaction 1 was protonated and the resulting [endo-3-2H]1 recycled. Reaction 2 cannot be monitored under these conditions. Reactions 1 and 3, and by inference also reaction 2, were almost completely suppressed when analogous reductions were carried out in the presence of ammonium chloride, [3,3-2H2]2 and [3,3-2H2]3 being obtained almost exclusively, in a 6: 94 ratio. It is proposed that the mechanism outlined in House [1] was dominant when, and only when, ammonium ion was the proton source; it may have competed when water was the proton source.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19810640717
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