syn-β-Acyloxy-ketones 6 and an anti-β-acyloxy-ketone 17 undergo smooth intramolecular enolate/ester condensations 6 18 and 17 19 when treated with TiCl4/EtN(i-Pr)2. Thus, tri- and tetrasubstituted cis- or trans-2,3-dihydro-4H-pyran-4-ones are easily prepared in a stereoselective manner.
当用TiCl 4 / EtN(i-Pr)2处理时,合成-β-酰氧基酮6和抗-β-酰氧基酮17会经历平滑的分子内烯醇酸酯/酯缩合6 18和17 19。因此,容易以立体选择性的方式制备三和四取代的顺式或反式-2,3-二氢-4 H-
吡喃-4-酮。