Synthesis, Reactivity, and Application as Chiral Auxiliaries of the novel (3 R )‐ and (3 S )‐4,5‐dihydro‐3‐hydroxy‐4,4,5,5‐tetramethyl‐3‐phenylfuran‐2(3 H )‐ones in the Paterno ‐ Büchi reaction

Both enantiomers of the novel α‐hydroxy‐γ ‐lactone (±)‐ 3 (4,5‐dihydro‐3‐hydroxy‐4,4,5,5‐tetramethyl‐3‐phenylfuran‐2(3 H )‐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 ‐ Büchi reaction) involving conventional separation of diastereoisomers ( 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 (−)‐(1 S , 4 R )‐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 , ( S )‐ 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 ‐ Büchi reaction of 2,3‐dimethylbut‐2‐ene to the benzoylformate ( S )‐ 7 ( = ( S )‐ 1d ; obtained from ( S )‐ 3 ) was shown to proceed with 58% de at 60°, leading to a decrease of enantiomeric purity in the hydrolysis product 3 .