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5.2.25.1.4 Variation 4: Using Other Alkenyl Anions

DOI: 10.1055/sos-SD-005-00498

Crisp, G. T.Science of Synthesis, (20035524.

The hydroalumination of substituted prop-2-yn-1-ols, followed by the addition of electrophilic trialkylstannanes, provides ready access to a variety of functionalized Z-alkenylstannanes. For example, addition of lithium aluminum hydride to propargyl alcohol selectively affords the Z-alkenylaluminate 11, which can be reacted with tributyltrifluoromethylsulfonyloxy)stannane (X=OTf) to give (Z)-3-(tributylstannyl)prop-2-en-1-ol (12, R1=H) in 80% yield (Scheme 6).[‌15‌] The hydroalumination of substituted prop-2-yn-1-ols can be used to prepare 3-substituted 3-(tributylstannyl)prop-2-en-1-ols 12 when tributylmethoxystannane (X=OMe) is used (lower yields are obtained with tributyltrifluoromethyl(sulfonyloxy)stannane or tributylchlorostannane) (Scheme 6).[‌16‌] Yields are in the range 1374% for a wide variety of R1 groups (alkyl, aryl, heteroaryl, ethers) and triethylamine should be added to the solvents used for chromatographic purification of the products in order to prevent protiodestannylation.[‌16‌] An alternative method for the preparation of γ-hydroxyalkenylstannanes, such as 13, is to use dichlorobis(η5-cyclopentadienyl)titanium to catalyze the hydromagnesiation of a propargyl alcohol, with subsequent trapping of the alkenylmagnesium intermediate with tributylchlorostannane (Scheme 6).[‌17‌] This method relies on the coordination of the metal to the oxygen to control the regio- and stereochemistry of the final alkenylstannane.

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