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Novel use of borate protective groups in organic synthesis. A facile synthesis of dihydro-β-santalol

✍ Scribed by Wayne I. Fanta; William F. Erman

Publisher
Elsevier Science
Year
1969
Tongue
French
Weight
194 KB
Volume
10
Category
Article
ISSN
0040-4039

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✦ Synopsis

Although methods for preparing boric acid esters have been known for many years (l), this means of protecting hydroxyl groups has found very limited practical use particularly in the field of organic synthesis.* We wish to communicate here the conversion of several complex alcohols to borates and subsequent utilization of these borates in hydrobromination, alkylation, and Wittig reactions where protection of a hydroxyl group was required. More specifically, we have applied these reactions to the synthesis of dihydro-g-santalol (I), a material with.the powerful, woody fragrance of East Indian sandalwood oil (2). We also record here a novel Meerwein-Pondorf reduction discovered during these synthetic studies. .The basic system of santalol I can be constructed by alkylating methyl norcamphor with the appropriate six carbon side chain. The required alkylation agent seemed most easily obtained from alcohol II (3) by protection of the hydroxyl group and subsequent anti-Markownikoff hydrobromination of the terminal unsaturation. Chart I depicts the stepwise sequence required to construct dihydro-B-santalol. Although several standard blocking groups (acetate, tetrahydropyranyl ether) did find a place in this work,** we found protection of the alcohol as the boric *

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