Highly chemoselective triple bond reductions on unsymmetrical 1,4-diorganyl-1,3-butadiynes

Abstract

Unsymmetrical 1.4-diorganyl-1,3-butadiyncs la-g undergo rcgio-, stereo- and chemoselective addition of butyltcllurolatc anion leading to ( Z)-1-butyltelluro-1,4-bis(organyl)but-1-en-3-ynes 2a-g in good yields. The terminal triple bond reacts faster than the propargylic triple bond (alcohol derivatives), which is more reactive than the triple bond bearing an alkyl or aryl group. Combination with removal of butyl tellurium moiety from the products obtained is equivalent to a chemoselective trans-hydrogenation of one triple bond of 1,3-butadiyncs Treatment of 2c or 2f with n-butyllithium in THF at −78 °C furnished the corresponding ( E)-cnynes free of tellurium 7a and 7b, respectively. Detelluration occurs with absolute retention of the double bond geometry In this way. sequential treatment with dimethyl sulfate of enynyl lithium 8 generated in situ by reaction of 2b with n-butyllithium produced the ( Z)-enyne free of tellurium 9 The reaction of 8 with CO 2 followed by acidification of the reaction mixture resulted in the formation of carboxylic acid 10 also with the central carbon-carbon double bond of Z configuration.