The Effect of Protecting Groups on Thallium(III)-Promoted Ring Contraction of 3-Alkenols

Abstract

2-(3,4-Dihydro-1-naphthalen-1-yl)propan-1-ol was protected with several groups. The reaction of these alkenol derivatives with thallium trinitrate (TTN) was then investigated. Oxidation of the methyl, benzyl and 4-phenylbenzyl ether led to the ring contraction product, as a single diastereomer, in reasonable yields (63-71%). The high diastereoselectivity can be explained by coordination between thallium(III) and oxygen during the rearrangement step. When treated with TTN under similar conditions, the acetate and benzoate derivatives were recovered unchanged. However, using excess of the oxidant, these esters led to indans as a 1:1 mixture of diastereomers, in 12-24% yield, together with a naphthalene derivative, in 9-24% yield. Treatment of the silyl ether derivatives with TTN promotes the cleavage of the protecting group, yielding the starting alkenol, which underwent oxidation, furnishing the expected indan in 37-57%.

Key words

thallium trinitrate - ring contraction - indans - alkenols - protecting groups

References

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12

The yield was calculated considering the molecular weight of the main product.

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