Arylmagnesium Bromide Additions to 1-Tetralone-2-acetic Acid Followed by Catalytic Hydrogenolysis: Stereochemical Consequences

A Stork reaction route (7 → 1b) was utilized to synthesize 1-tetralone-2-acetic acid methyl ester (1a) from 1-tetralone. Addition of a 2′-(o-methoxyphenyl) magnesium bromide to this ketone followed by palladium-catalyzed hydrogenation of the intermediate cis lactones (2, verified by X-ray crystal structure determination of 2a, Figure 1), afforded predominantly a 1,2-cis tetralin (3) accompanied by smaller yields of the corresponding 1,2-trans tetralin (4). The stereochemical consequences of this reaction sequence was unequivocally established by X-ray crystal structure elucidation of 1,2-cis methyl ester 3b (Figure 2) and 1,2-trans carboxylic acid 4a (Figure 3). Stereochemical assignments for the analogous diastereoisomeric sets 3c-f and 4c-f were obtained by high-field (400-MHz) ¹H and ¹³C NMR correlations with the crystal structures. The overall reaction pathway illustrates a useful approach to 1,2-cis-alkylated tetralins and certain sterically hindered 1,2-trans-alkylated tetralins.