Studies on deoxygenation of decane-1,2-diol derivatives with pinacol-derived chlorohydrosilane
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Tutkimus dekaani-1,2-diolijohdannaisten deoksygenoimiseksi pinakoliperäisen kloorihydrosilaanin avulla
In spite of the extensive studies, which have been carried out on the selective deoxygenation of secondary alcohols, it still poses a formidable challenge. The recent discovery of the reduction of salicylaldehydes with a system of a pinacol-derived chlorohydrosilane (PCS) and a Lewis base prompted the idea of adapting the procedure in the selective deoxygenation of vicinal diols. The most viable option of attaining such deoxygenations, after a thorough study of available literature, was to convert the hydroxyl groups to better leaving groups, to facilitate an intramolecular hydride delivery from PCS. Based on this hypothesis, the potential of PCS in the selective deoxygenation of decane-1,2-diol derivatives was investigated. It was decided that the main focus of the project would be on the attempted deoxygenations of the secondary hydroxyl group of decane-1,2-diol, which required the syntheses of several secondary diol derivatives. The preparation of the secondary derivatives was carried out using a three-step pathway, where the primary hydroxyl group of the diol was ﬁrst protected as a tert-butyldimethylsilyl (TBDMS) ether, after which the secondary hydroxyl group was functionalized. In the ﬁnal step, the TBDMS-group was removed to restore the primary hydroxyl group. The secondary hydroxyl group of decane-1,2-diol was successfully converted into tosylate and carbamate groups. The conversions of the secondary hydroxyl group into trichloroacetate and ethyl malonate moieties were also accomplished, although unintentional intramolecular transesteriﬁcation during the deprotections resulted in the formation of mixtures of two regioisomers, which were used directly as starting materials in the deoxygenation stage due to isomer separation issues. Finally, the direct tosylation of the primary hydroxyl group was also performed with success, without the use of a protecting group. The deoxygenations of the prepared intermediates were then attempted, using the combination of PCS and Lewis bases. Despite the various conducted experiments and the screening of a variety of Lewis bases for optimal catalytic activity, the deoxygenation of the synthetized decane-1,2-diol derivatives was not achieved. However, this work may serve as a reference point for future attempts of investigating other alternatives, where deoxygenations of this nature could be accomplished.