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35.2.2.1.1 Method 1: Substitution of Hydroxy Groups

DOI: 10.1055/sos-SD-035-00385

Braun, M.Science of Synthesis, (200735387.

In most cases, propargylic alcohols serve as the starting materials for the preparation of propargylic bromides; however, drastic and highly acidic conditions should be avoided because they can lead to the formation of rearranged allenyl bromides or unsaturated carbonyl compounds by MeyerSchuster or Rupe rearrangement (see HoubenWeyl, Vol.5/2a, pp665668). The most frequently applied reagents for the conversion of propargylic alcohols into bromides are phosphorus tribromide, triphenylphosphine/bromine, or triphenylphosphine/carbon tetrabromide. Illustrative examples are given in Table 1.[‌3‌‌15‌] The combination of triphenylphosphine and carbon tetrabromide causes the propargylic carbinol center to react under complete inversion.[‌11‌,‌12‌] When applied to tetrahydropyranyl-protected propargylic alcohols, the treatment with triphenylphosphine and bromine leads to propargylic bromides directly.[‌16‌‌19‌] Because the procedures are essentially analogous to those described in Section 35.2.1.5, only selected examples are given here. Further reagents suitable for the conversion of propargylic alcohols into bromides are triphenyl phosphite/bromine,[‌20‌] 1,2-bis(diphenylphosphino)ethane/bromine,[‌21‌,‌22‌] and, after formation of the silyl ether, bromotrimethylsilane.[‌23‌]

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