Access to highly functionalized cyclopentenones via diastereoselective Pauson−Khand reaction of siloxy-tethered 1,7-enynes

Abstract

Propargyl alcohols S23 -S25 purchased commercial sources and used as is without further purification. B. 1,7-Siloxy-Tethered Enynes General Procedure 1: 1,7-Siloxy-Tethered Enyne SynthesisA flame dried round-bottom flask equipped with a magnetic stir-bar was sequentially charged with dry CH 2 Cl 2 (0.5 M with respect to the propargyl alcohol), allyldiisopropylchlorosilane S21 29 (1.2 equiv), DMAP (0.2 equiv), and NEt 3 (2.0 equiv) under an inert atmosphere (N 2 ). The reaction mixture was cooled to 0 °C. In a separate flame-dried pear-shaped flask, the propargyl alcohol (S1 -S20 and S23 -S25; 1.0 equiv) was dissolved in CH 2 Cl 2 (1.0 M) and added dropwise to the 0 °C reaction mixture via syringe. This was followed by rinsing the pear-shaped flask with an additional portion of CH 2 Cl 2 (0.3 mL). The cooling bath was removed, and the reaction mixture allowed to stir at room temperature (25 o C) for 18 h. Upon consumption of the propargyl alcohol, as noted by TLC analysis, the reaction mixture was quenched with sat. aq. NH 4 Cl. The aqueous phase was extracted with CH 2 Cl 2 (3x 20 mL), and the combined organic phases were washed with brine, dried with MgSO 4 , filtered, and concentrated under reduced pressure. Flash chromatography (hexanes -0.25% Et 2 O/hexanes) yielded enynes 1a-j and 5a-k as colorless oils.