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Alcohol Protecting Groups - Chemistry LibreTexts
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Alcohol Protecting Groups
For Members. All compounds were obtained in good yields and purified by distillation. Compounds 1 - 6 were then subjected to hydrotelluration conditions 11 to yield the corresponding regioisomeric vinyl tellurides A and B. The obtained results are shown on Table 1. When 1 was used as the alkyne source an almost mixture of regioisomers A and B was observed Table 1 , entry 1. The influence of the protective group is remarkable.
In spite of the widespread use of bulky groups in organic chemistry, there are few attempts at quantifying the intuitive concept of bulkiness. The influence of the temperature on the reaction was also studied.
This fact might be due to the lower reactivity of the involved species at this temperature. The two regioisomeric tellurides A and B were obtained under different conditions, with vinyl telluride A predominating at higher temperature. This fact should indicate that the telluride A might be the thermodynamic product. Therefore, vinyl telluride B would be the kinetic product or the product of kinetic control since it should be formed faster at lower temperatures. To test this hypothesis, a mixture of tellurides A and B were stirred in EtOH under reflux during 2 h.
No change in the ratio of the products was observed, even when an additional amount of sodium borohydride was added. The effect of the distance of the hydroxyl moiety from the triple bond, as well as the influence of a substituted propargylic alcohol on the ratio of the products were also studied Scheme 2.
The results are depicted in Table 2. Lower regioselectivities were observed for the unprotected alcohols Table 2 , entries 1 and 2.
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It is interesting to note that when 9 was used as the alkyne source; only one regioisomer was obtained Table 2 , entry 3. Our approach for the synthesis of Seselidiol started with 1-octanol 11 which was oxidized into the corresponding aldehyde 12 using PCC. It is noteworthy that when the hydrotelluration reaction was performed without TIPS as the protective group a mixture of of the two regioisomers were observed. In summary, the methodology presented is shown to be useful for the synthesis of regio- and stereo-defined vinyl tellurides, the TIPS group being successfully used as a regio-directing group.
The application of the methodology to the synthesis of a natural product was performed in order to demonstrate its applicability. Finally, the methodology offers future possibilities in the development of new organometallic approaches to the compounds containing Z -double bonds.
Related Protecting groups
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