(+)-Camphor Bromide synthesis

Yield: 82%

Reaction Conditions:

with bromine;acetic acid at 20 - 90;

Steps:

(1R, 3S, 4S)-3-Bromo-1,7,7-trimethylbicyclo[2.2.1]heptan-2-one 11⁴
Acetic acid (50 mL) was added to (+)-camphor 10 (20 g, 131 mmol) in a 3-neck flask. The solution was heated under reflux at 80-90 ^oC and a solution of bromine (8 mL, 155 mmol) in acetic acid (8 mL) was added slowly in small aliquots to prevent the deep red colour of excess bromine building up. The solution was heated under reflux at 80-90 ^oC for a further 2 h and then allowed to cool to room temperature and stirred overnight. The mixture was then added dropwise with stirring to ice/water (120 mL). The resulting precipitate was filtered off and washed with 20 mL portions of water until the filtrate was colourless. The solid was sucked dry on the Buchner funnel and left to dry in the air for a day. The solid was then taken up in ether, dried, filtered and concentrated under reduced pressure to afford the title compound as a white solid (24.85 g, 82 %). m.p.: 75 ^oC (from ether); Lit.⁵: 76 ^oC. [α]_D (c 1.01, MeOH, 22 ^oC) +125.7; Lit.⁵: (c 1.0, 23 ^oC) +125. IR: _max (N) 2921, 1761 (C=O), 1459, 1375, 1318, 1274, 1208, 1105, 1034, 1003, 911, 808, 767, 691 cm^-1. ¹H NMR (400.1 MHz; CDCl₃; Me₄Si): 0.95 (3H, s, 1-CH₃), 0.99 (3H, s, 7-CH₃), 1.09 (3H, s, 7-CH₃), 1.41-1.48 (1H, m), 1.65-1.74 (1H, m), 1.85-1.94 (1H, m), 2.07-2.13 (1H, m), 2.32 (1H, t, ³J = 4.7, 4-CH), 4.64 (1H, d, ³J = 4.7, 3-CH exo) ppm. ¹³C NMR (100.6 MHz; CDCl₃; Me₄Si): δ 9.1 (1-CH₃), 19.4 (7-CH₃), 19.5 (7-CH₃), 21.9 (C-5), 30.0 (C-6), 45.4 (C-7), 49.1 (C-4), 53.4 (C-3), 57.1 (C-1), 212.1 (C-2) ppm. HRMS (CI) m/z 253.0213: calculated for [C₁₀H₁₅OBr + Na]⁺ 253.0203.

References:

Lewis, Frank W.;McCabe, Thomas C.;Grayson, David H. [Tetrahedron,2011,vol. 67,# 39,p. 7517 - 7528] Location in patent:supporting information; experimental part