No abstract

3,3,4,4-Tetraethoxy-1-butyne, available in high yield in four simple steps from ethyl vinyl ether, is a highly functionalized alkyne, which appears to be a versatile starting material for the synthesis of a range of alkylated, more-or-less deoxygenated carbohydrate mimics. However, many of the reactions used to achieve extension and subsequent structural modification of the carbon chain as well as removal of the protecting groups turn out to be rather sensitive to the substituents' steric and electronic influence. As a result, the reactivity pattern that emerges is somewhat complex.

1-Substituted 4,4,5,5-tetraethoxy-2-pentyn-1-ols undergo stereospecific reduction to allylic and homoallylic alcohols under the right conditions. Hydrogenation over Lindlar's catalyst gave the corresponding (Z)-allylic alcohols in excellent yield provided potassium carbonate was added. Reduction was also achieved with lithium aluminum hydride, but the product appeared to be solvent and temperature dependent. In THF at -15 o C the corresponding (E)-allylic alcohols were formed, in better than 70% yield from secondary propargylic alcohols, but below 60% from tertiary ones; in refluxing diethyl ether the products were the corresponding 1-substituted derivatives of homoallylic alcohol (E)-4,5,5-triethoxypent-3-en-1-ol, obtained in 93% yield in the best case.

Ethyl vinyl ether Benzyltriethylammonium chloride 1, 1‐Dichloro‐2‐ethoxycyclopropane Copper sulfate pentahydrate

Selected members of the title family of compounds, prepared from 1,1-dibromo-2-chloro-2-diethoxymethylcyclopropane by standard chemical transformations, were dissolved in mixtures of dichloromethane and a protic, nucleophilic reagent and treated with 50% aqueous sodium hydroxide in the presence of a phase-transfer catalyst, triethylbenzylammonium chloride (TEBA), at room temperature. In all cases except two, regiospecific ring opening of the cyclopropane took place, giving one product formed by nucleophilic attack of the carbon atom to which the polar substituent was attached. This clearly lends support to the notion that hydrogen bonding contributes significantly to direct the attack of protic nucleophiles.