Acetone → (3aS,5S,6aR)-5-(tert-Butoxycarbonylamino)hexahydro-2H-cyclopenta[b]furan-3a-carboxylic acid

Participants

Reaction Conditions

Reaction Steps

A 22-L four-neck round bottom flask equipped with a mechanical stirrer, nitrogen inlet, 1-L addition funnel with nitrogen outlet, a temperature probe, and an external bath for cooling was purged with nitrogen overnight. A solution of the product of Step D (426 g, 1.57 mol) and acetone (8.1 L) was added, the flask was cooled to 7° C., and the addition funnel was charged with Jones reagent (710 mL). The oxidant was added dropwise over 1 h 20 min, keeping the temp between 7-9° C. After the first 200 mL was added, a green ball formed that made stirring very difficult. After about ½ of the oxidant was added, LCMS was run to follow the reaction. At the end of addition, olive green suspension resulted with a hint of red (excess Jones). The ice bath was removed, the reaction was stirred at rt for 1 h after which time the reaction was judged complete. Isopropyl alcohol (40 mL) was added, the reaction stirred for 25 min, and water (800 mL) was added, that caused a nice separation of green chunk from the acetone/water layer. The water/acetone was decanted off and evaporated. The green chunk was dissolved in water (1.5 L), transferred to a separatory funnel and extracted with CH2Cl2 (1 L). The aqueous layer was checked by TLC and found to contain no product, so it was discarded. The organic extract was saved for combining later. The green water/acetone concentrate was evaporated to about 5-7 L, until the solution looked hazy. The concentrate was transferred to a separatory funnel and extracted with CH2Cl2 (1×3 L, 3×1 L) and the aqueous layer checked after each extraction for the presence of product. The combined extracts were washed with brine (250 mL) which caused a terrible emulsion. The emulsion was broken by addition of water and EtOAc (˜500 mL). The organic layer was dried (Na2SO4) but not very effectively as some water came through during the filtration. Near the end of the evaporation, the distillation rate slowed, and a thick yellow oil resulted. MeCN (500 mL) was added to the pot, the rotary evaporator bath warmed to 50° C., and the contents seeded with reference material. A fine white solid slowly formed within 10 min or so. Seeding was done a second time, and continued swirling for another 10 min at 50° C. Crystallization was visually detected, the bath was drained and filled with ice, and the flask swirled at 0° C. for 30 min, resulting in a thick white solid. The solid was filtered, washed with ice-cold MeCN (2×100 mL) and the solid was air-dried overnight. The product of Step E was isolated as a white, free-flowing solid. 1H NMR (MeOH) δ: 4.43 (d, J=5.4 Hz, 1H), 4.00-4.13 (m, 1H), 3.89-3.98 (m, 1H), 3.63 (td, J=9.1, 5.7 Hz, 1H), 2.54 (ddd, J=12.6, 5.7, 3.2 Hz, 1H), 1.93-2.13 (m, 3H), 1.74-1.87 (m, 1H), 1.53-1.66 (m, 1H), 1.43 (s, 9H). Calculated for C13H21NO5: 294.1 (M+23). found: 294.1.

Provenance & Evidence