迄今已合成的3000多种1α,25-二羟基维生素D 3的类似物中,只有少数几个特征在于seco-B环的结构修饰。在C-6处烷基化的化合物似乎是合成努力的目标。这样的维生素D类似物容易经历热转化成其维生素原形式。分子建模的结果表明,与6-烷基取代基和C环中氢原子相互作用的分子中必须存在与平面性的显着偏离。1α,25-(OH)2 D 3的类似物的合成在此报道了以6-甲基为特征的H2O3,以及对其生物学潜能的初步测试结果。使用新颖的立体收敛策略有效地制备了这种6-烷基化的化合物,其中维生素D骨架的环A和三烯单元通过一锅Pd催化的串联环化-Negishi偶联过程构建。
An Expeditious Route to 1α,25-Dihydroxyvitamin D<sub>3</sub>and Its Analogues by an Aqueous Tandem Palladium-Catalyzed A-Ring Closure and Suzuki Coupling to the C/D Unit
mild, general, and highly stereoselectivePd0‐catalyzed cascade to the triene system of the hormone 1α,25‐dihydroxyvitamin D3 and six representative analogues is reported. The intramolecular cyclization of an enol–triflate (lower fragment) followed in situ by Suzuki–Miyaura coupling with an alkenyl boronic ester (upper fragment, also efficiently prepared by Pd0‐catalyzed coupling) in equimolar amounts