A new practical synthesis of silyl enol ethers

The Enantioselective Tsuji Allylation

“…3,4 To a solution of sodium iodide (15.0 g, 100 mmol, 1.25 equiv) in ACN (125 mL) were added 2-ethylcyclohexanone (10.1 g, 80 mmol, 1.0 equiv), TEA (14.0 mL, 100 mmol, 1.25 equiv), and finally TMSCl (11.6 mL, 91.2 mmol, 1.14 equiv) in a dropwise fashion. After 1 h, pentane (75 mL) was added, the biphasic mixture was stirred for 2 min, and the pentane decanted.…”

“…Evaporation and chromatography (2 % Et 2 O in Hexanes on SiO 2 ) afforded the pure silyl enol ether (3.21 g, 40.5 % yield). 84.2 % OTMS CH 3 84.2 % yield of a ~10 : 1 mixture favoring the tetrasubstituted isomer was isolated after simple distillation. The minor isomer was removed by fractional distillation with a spinning band column.…”

“…A 50 mL rb flask equipped with a magnetic stir bar was flame dried under vacuum. After cooling under dry argon, Pd 2 (dba) 3 (22.9 mg, 0.025 mmol, 0.025 equiv) and (S)-t-Bu-PHOX (24.2 mg, 0.0625 mmol, 0.0625 equiv) were added. After the flask was flushed with argon, THF (30 mL) was added and the contents were stirred at 25 °C for 30 min, at which time allyl enol carbonate 1 (196.2 mg, 1.0 mmol, 1.0 equiv) was added by syringe in one portion.…”

“…The combined organics were dried (MgSO 4 ), concentrated, and chromatographed to give the ketal (1.59 g). The ketal in THF (15 mL) was added dropwise to a cooled (-25 °C) solution of BH 3 •THF (20.3 mmol, 2.5 equiv) in THF (100 mL), and after 4 h was allowed to warm to 25°C overnight. The reaction mixture was then cooled to -10 °C, water (25 mL) was slowly added, followed by NaBO 3 •4H 2 O (4.99 g, 32.4 mmol, 4.0 equiv), and the reaction mixture was allowed to warm to 25 °C.…”

Formal Synthesis of (±)-Allocolchicine Via Gold-Catalysed Direct Arylation: Implication of Aryl Iodine(III) Oxidant in Catalyst Deactivation Pathways

“…After conversion to a silyl enol ether, 7 [13], this is engaged in a retroBrook rearrangement [14] and the resulting lithium enolate alkylated by trimethoxy benzylbromide 8 to afford ortho-silyl arylketone 9 [15]. Reduction to alcohol 10, then O-alkylation with MOMBr leads to the pre-cyclisation scaffold 11.…”