Model Studies of Terpene Biosynthesis. Intermolecular 1'-2 Electrophilic Condensation of 3-Methyl-2-butenyl Acetate

Article abstract of DOI:10.1021/ja00369a044

The stereochemistry of the carbon-carbon bond-forming step in the electrophilic intermolecular 1'-2 condensation of 3-methyl-2-butenyl acetate (1-OAc) to yield lavandulyl acetate (2-OAc) was studied.Treatment of (1S)-<1-2H>3-methyl-2-butenyl acetate ((1S)-<1-2H>1-OAc) with aluminum trichloride in ethyl acetate gave labeled lavandulyl acetate (<1,3-2H2>2-OAc) (30percent) and isoprene (65percent) as the major products.The configurations at C(1), C(2), and C(3) and the relative abundances of the diastereomers of <1,3-2H2>1-OAc were determined by converting the mixture to <2,4-2H2>3-(2'-propyl)-butyrolactone (<2,4-2H2>3).The intensities of 1H resonances characteristic of each diastereomer were measured with the aid of Pirkle's chiral shift reagent, (S)-(+)-2,2,2-trifluoro-1-(9-anthryl)ethanol.The analysis showed that equal amounts of the (1S,2S,3R), (1S,2R,3R), (1S,2S,3S), and (1S,2R,3S) diastereomers of <1,3-2H2>2-OAc were obtained, signifying that the 1'-2 condensation was stereorandom at C(1) of the electrophilic isoprene unit.