Tetrahydrofuran → 1,3-Cyclopentadiene, 1-methyl-3-propyl-

Participants

Reaction Conditions

Reaction Steps

n-PrMgCl (2.0M in Et2O, 20 ml, 40 mmol) and THF (10 ml) were charged under nitrogen into a 100 ml, 3-necked, round-bottom flask equipped with a thermometer, magnetic stirring bar, and an addition funnel. The mixture was cooled to -10° C. in an ice/acetone bath. 3-Methyl-2-cyclopentenone (97%, 3.6 g, 36.4 mmol) was added into the PrMgCl at -10° to -5° C. over a period of 20 minutes. The reaction mixture was slowly warmed to 22° C. over a period of one hour. GC analysis of a small acidified sample (added into excess aqueous acetic acid at 5° to 15° C., pH=4.5) showed a >97% conversion of 3-methyl-2-cyclopentenone. The reaction mixture was then slowly added at <5° C. into aqueous acetic acid (4.66 g, 77.6 mmol of acetic acid in 14.0 g of water) over a period of 30 minutes to form 1-methyl-3-n-propylcyclopentadiene via the dehydration of the 1-propyl-3-methyl-2-cyclopenten-1-ol intermediate. The pH of the aqueous layer was 4.5. The reaction mixture was stirred at 36° C. for 1 hour to complete the dehydration reaction. GC analysis indicated a >97% conversion of 1-propyl-3-methyl-2-cyclopenten-1-ol and the formation of 1-methyl-3-n-propylcyclopentadiene (with 28% exo isomers). The aqueous layer was phase cut. The organic layer, which weighed 29.2 g, was washed at 5° C. with aqueous Na2CO3 solution (2.42 g, 22.8 mmol of Na2CO3 in 10.0 g of water). The pH of the aqueous layer was 9.0. After phase cutting the aqueous layer, the organic layer weighed 25.4 g. Proton NMR (with CH2Br2 as internal standard) indicated that the yield of 1-methyl-3-n-propylcyclopentadiene was 77±4%. The structure of 1-methyl-3-n-propylcyclopentadiene was confirmed by GC/MS.

Provenance & Evidence