Yield:924871-41-0 78%

Reaction Conditions:

Stage #1: 7-methyl-2,3-dihydrobenzo[b][1,4]dioxine-6-carbaldehydewith potassium permanganate in water; for 4 h;
Stage #2: with potassium hydroxide in water at 20;
Stage #3: with hydrogenchloride in water;

Steps:

9.C

Step C: Synthesis of 7-methyl-2,3-dihydrobenzo[b][1,4]dioxine-6-carboxylic acid; A mixture of 7-methyl-2,3-dihydrobenzo[bb][1,4]dioxine-6-carbaldehyde (2.0 g, 11.2 mmol) in water (100 mL) was heated to 70° C. and stirred for 1 h. Potassium permanganate (2.3 g, 14.6 mmol) in water (50 mL) was then added portion wise over 4 h. After this time, the mixture was cooled to room temperature and 10% potassium hydroxide (50 mL) was then added. The solids were removed by filtration and washed with water (100 mL) and the basic solution then acidified with 2 N hydrochloric acid. The precipitate that formed was collected by filtration, washed with water, and dried in a vacuum oven overnight to afford 7-methyl-2,3-dihydrobenzo[b][1,4]dioxine-6-carboxylic acid (1.7 g, 78%) as a white solid: 1H NMR (500 MHz, DMSO-d6) δ 12.49 (s, 1H), 7.33 (s, 1H), 6.76 (s, 1H), 4.25 (m, 4H), 2.40 (s, 3H).

References:

US2009/312323,2009,A1 Location in patent:Page/Page column 18-19