AbstractAn efficient synthesis of cyclohexenes has been achieved from easily accessible tetrahydropyrans via a tandem 1,5‐hydride shift–aldol condensation. We discovered that readily available aluminium reagents, e.g. Al2O3 or Al(OtBu)3 are essential for this process, promoting the 1,5‐hydride shift with complete regio‐ and enantiospecificity (in stark contrast to results obtained under basic conditions). The mild conditions, coupled with multiple methods available to access the tetrahydropyran starting materials makes this a versatile method with exceptional functional group tolerance. A wide range of cyclohexenes (>40 examples) have been prepared, many in enantiopure form, showing our ability to selectively install a substituent at each position around the newly forged cyclohexene ring. Experimental and computational studies revealed that aluminium serves a dual role in facilitating the hydride shift, activating both the alkoxide nucleophile and the electrophilic carbonyl group.
摘要 通过串联 1,5-酸酐转移-醛醇缩合,从容易获得的四氢吡喃中高效合成了环己烯。我们发现,铝试剂(如 Al2O3 或 Al(OtBu)3)在这一过程中非常重要,可促进 1,5-酸酐转移,并具有完全的区域特异性和对映体特异性(与在碱性条件下获得的结果形成鲜明对比)。温和的条件加上多种获得四氢吡喃起始材料的方法,使该方法成为一种具有特殊官能团耐受性的多功能方法。我们已经制备出了多种环己烯(40 个实例),其中许多是对映体,这表明我们有能力在新形成的环己烯环周围的每个位置选择性地安装一个取代基。实验和计算研究表明,铝在促进氢化物转移方面起着双重作用,既能激活亲氧化烷基的亲核体,又能激活亲电羰基。