Diastereomerically pure rarely functionalized alkenoyl dihydropyrans, 1,6-diketones, and cyclopentanes from acetylene gas and ketones

Pure ( E )-alkenoyl dihydropyrans are stereoselectively assembled from 2-acetyl-3,4-dihydropyrans (products of one-pot self-organization of acetylene gas and ketones) and aromatic aldehydes (52-86% yields). Furthermore, ( E )-alkenoyl dihydropyrans undergo ring opening (acid hydrolysis) to afford 5-hydroxy-1,6-diketones (44-67% yields) and acetyl-2-( E )-styryl-2,3-dihydroxycyclopentanes (19-32% yields), both as single diastereomers. Alkenoyl dihydropyrans stereoselectively assembled from acetylene gas, ketones and aldehydes in two steps are diastereoselectively transformed into difficult-to-access, rarely functionalized 1,6-diketones and cyclopentanes.