p-Toluenesulfonic acid monohydrate → (R)-(-)-2,2-Dimethyl-3-(1-methylethylidene)cyclobutanecarboxylic acid

Participants

Reaction Steps

A solution of 3.68 g (21.9 mmol) of 4a in 60 mL of benzene with 416 mg (2.19 mmol) of p-toluenesulfonic acid monohydrate was heated in an oil bath at 100-110° C. for 24 h. A mini Dean-Stark trap was used for azeotropic distillation. Benzene was evaporated on a rotary evaporator, and the residue was treated with 2N aqueous Na2CO3 solution. The basic aqueous solution was washed with ether, then acidified to pH 2 with hydrochloric acid, and again extracted with ether. The combined ether extracts were washed with water, brine, dried, and concentrated to give 2.87 g (17.1 mmol, 78% yield) of 5a as clear oil after chromatography (silica gel, eluted with 20% to 25% of ethyl acetate in hexanes). Optical purity: 79% ee (after methylation); [α]24D−22.0 (c 0.1, MeOH); 1H NMR (CDCl3): δ 1.19 (3H, s), 1.37 (3H, s), 1.48 (3H, s), 1.58 (3H, s), 2.55 (1H, m), 2.81 (2H, m); 13C NMR (C6D6): δ 183.49, 135.57, 123.27, 47.47, 45.09, 28.15, 25.94, 22.09, 19.51, 18.52; EI-MS m/z (%): 168 [M]+ (38), 153 (38), 135 (8), 125 (21), 123 (27), 107 (59), 93 (29), 81 (100), 67 (30), 53 (16), 41 (25); HREIMS: obsd. 168.1152, calcd. for C10H16O2 (M+): 168.1150.

Provenance & Evidence