[36551-06-1] · C11H20O2Si · 3-Tetrahydropyranyloxy-1-trimethylsilyl-1-propyne · (MW 212.40)
Physical Data: bp 108 °C/11 mmHg; n
Solubility: sol THF, ether, and most organic solvents.
Handling, Storage, and Precautions: store in the absence of air and moisture.
The ambident character of the propargylic anion, which may be in equilibrium with the allenic form, is responsible for its limited use in synthesis. In general the structure and reactivity of the ambident anion depend on the nature of the substrate, the counter cation, and the solvent.7,8 There is also an erythro-threo stereoselectivity problem when alkylated propargylic anions react with aldehydes or unsymmetrical ketones. In contrast, the zinc and titanium reagents derived from the title compound possess the allenic structure and, upon reaction with aldehydes, lead almost exclusively to the b-acetylenic alcohol (eq 1), presumably by a chelate transition state (SEiŽ process).3,5 The reaction also leads preferentially to the erythro diastereomer. The stereoselectivity is highest with titanium as the metal and THF as the solvent.6,9
Whereas the titanium reagent is not reactive towards ketones, the zinc derivative has been found to react even with sterically encumbered ketones, such as 17-keto steroids, to yield the b-acetylenic alcohol in good yield (75%).2
The title compound can be used in reductive alkylation sequences for the synthesis of functionalized vinylsilanes with high isomeric purity (eq 2). One sequence consists of a regioselective cis-hydroboration, transmetalation, and carbodemetalation.4,10 In another sequence, Diisobutylaluminum Hydride reduction-bromination leads to brominated vinylsilanes,11 which can be further transformed via halogen-metal exchange, followed by reaction with iodides,12 or with aldehydes and ketones.13
Pierre J. De Clercq & Frank Nuyttens
Universiteit Gent, Belgium