Synthesis ( IF 2.2 ) Pub Date : 2018-04-18 , DOI: 10.1055/s-0037-1609688
Arndt Hausherr 1 , Hans-Ulrich Reissig 1
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Dedicated to Professor Manfred Braun on the occasion of his 70th birthday
Abstract
Two routes to 3-alkyl-substituted 1-alkoxyallenes are investigated. The deprotonation and alkylation at C-3 of methoxyallene requires prior silylation at C-1 and provides mixtures of the expected products and 1-alkyl-substituted methyl propargyl ethers as minor component. The desilylation of these mixtures affords the desired 3-alkyl-substituted 1-methoxyallenes together with the 1-alkyl-substituted isomers in moderate overall yields. Following the second route, the disadvantages of this three-step method are avoided. In analogy to Brandsma, C-3 alkylation of methyl propargyl ether and subsequent isomerization under basic conditions affords two of the desired 3-alkyl-substituted methoxyallenes in good yields. This method is also applied to propargyl ethers bearing a diacetone-fructose-derived auxiliary. Two diastereomeric 3-alkyl-substituted 1-alkoxyallenes are formed during the isomerization, the ratio being strongly dependent on the reaction conditions. The mechanistic aspects of these observations are discussed on the basis of deuteration experiments and the configurational stability of the ambident propargyl-allenyl carbanion involved.
Two routes to 3-alkyl-substituted 1-alkoxyallenes are investigated. The deprotonation and alkylation at C-3 of methoxyallene requires prior silylation at C-1 and provides mixtures of the expected products and 1-alkyl-substituted methyl propargyl ethers as minor component. The desilylation of these mixtures affords the desired 3-alkyl-substituted 1-methoxyallenes together with the 1-alkyl-substituted isomers in moderate overall yields. Following the second route, the disadvantages of this three-step method are avoided. In analogy to Brandsma, C-3 alkylation of methyl propargyl ether and subsequent isomerization under basic conditions affords two of the desired 3-alkyl-substituted methoxyallenes in good yields. This method is also applied to propargyl ethers bearing a diacetone-fructose-derived auxiliary. Two diastereomeric 3-alkyl-substituted 1-alkoxyallenes are formed during the isomerization, the ratio being strongly dependent on the reaction conditions. The mechanistic aspects of these observations are discussed on the basis of deuteration experiments and the configurational stability of the ambident propargyl-allenyl carbanion involved.
中文翻译：
3-烷基取代的1-烷氧基丙二烯的制备-合成和机理方面
专用于曼弗雷德·布劳恩教授在他的70之际个生日
抽象的
研究了3-烷基取代的1-烷氧基丙二烯的两种途径。甲氧基烯丙基在C-3处的去质子化和烷基化需要在C-1处进行预先的甲硅烷基化，并提供预期产物和1-烷基取代的甲基炔丙基醚的混合物作为次要组分。这些混合物的甲硅烷基化以适中的总收率提供了所需的3-烷基取代的1-甲氧基丙二烯与1-烷基取代的异构体。遵循第二条路线，可以避免这种三步法的缺点。与Brandsma类似，甲基炔丙基醚的C-3烷基化和随后在碱性条件下的异构化以良好的产率提供了两个所需的3-烷基取代的甲氧基烯丙基。该方法也适用于带有双丙酮果糖衍生助剂的炔丙基醚。在异构化过程中形成两个非对映异构的3-烷基取代的1-烷氧基丙二烯，该比例强烈取决于反应条件。在氘化实验的基础上讨论了这些观察结果的机械方面，还涉及了周围的炔丙基-烯丙基碳负离子的构型稳定性。
研究了3-烷基取代的1-烷氧基丙二烯的两种途径。甲氧基烯丙基在C-3处的去质子化和烷基化需要在C-1处进行预先的甲硅烷基化，并提供预期产物和1-烷基取代的甲基炔丙基醚的混合物作为次要组分。这些混合物的甲硅烷基化以适中的总收率提供了所需的3-烷基取代的1-甲氧基丙二烯与1-烷基取代的异构体。遵循第二条路线，可以避免这种三步法的缺点。与Brandsma类似，甲基炔丙基醚的C-3烷基化和随后在碱性条件下的异构化以良好的产率提供了两个所需的3-烷基取代的甲氧基烯丙基。该方法也适用于带有双丙酮果糖衍生助剂的炔丙基醚。在异构化过程中形成两个非对映异构的3-烷基取代的1-烷氧基丙二烯，该比例强烈取决于反应条件。在氘化实验的基础上讨论了这些观察结果的机械方面，还涉及了周围的炔丙基-烯丙基碳负离子的构型稳定性。
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