Synthesis, Reactivity, and Application as Chiral Auxiliaries of the Novel (3R)- and (3S)-4,5-Dihydro-3-hydroxy-4,4,5,5-tetramethyl-3-phenylfuran-2(3H)-ones in the Paterno-Buechi Reaction

Article abstract of DOI:10.1002/hlca.19890720815

Both enantiomers of the novel α-hydroxy-γ-lactone (+/-)-3 (4,5-dihydro-3-hydroxy-4,4,5,5-tetramethyl-3-phenyfuran-2(3H)-one) have been synthesized via hydrolysis of the oxetanes 2 derived from the photochemical <2 + 2> cycloaddition of the ketones 1 and 2,3-dimethylbut-2-ene (Paterno-Buechi reaction) involving conventional separation of diastereisomers (Schemes 2 and 3).The absolute configuration of (R)- and (S)-3 and of the corresponding oxetane precursors could be assigned on the basis of an X-ray structural analysis of the (-)-(1S,4R)-camphanoyl derivative (3'S)-5 of (S)-3.O-acylation of (S)- and (+/-)-3 to yield a variety of derivatives ((3'S)- and (3'RS)-5 and (+/-)-7, (+/-)-8, (+/-)-9) was accomplished by deprotonation with BuLi at room temperature and subsequent quenching of the Li alcoholate with acyl chlorides or acid anhydrides, demonstrating the extraordinary chemical stability of 3.Additionally, the course of the temperature-dependent diastereoselective Paterno-Buechi reaction of 2,3-dimethylbut-2-ene to the benzoylformate (S)-7 ( = (S)-1d; obtained from (S)-3) was shown to proceed with 58 percent de at 60 deg C, leading to a decrease of enantiomeric purity in the hydrolysis product 3.