Oxonium salt alkylation of structurally and optically labile alcohols

Synthesis and Transformations of 5‐Chloro‐2,2′‐Dipyrrins and Their Boron Complexes, 8‐Chloro‐BODIPYs

“…BODIPYs 5a , b were also obtained from dipyrrylketones 1a , b upon reaction with Meerwein’s salt (triethyloxonium tetrafluoroborate). [21] Treatment of 1a and 1b with Meerwein’s salt in chloroform, at room temperature, gave orange-red colored solutions, indicating the formation of the fully conjugated 5-ethoxy-dipyrrins. After aqueous workup, the crude residues were complexed with boron by using similar conditions to those reported above, to produce BODIPYs 5a , b in 71–82% overall yields (Scheme 1).…”

Design, asymmetric synthesis, and evaluation of pseudosymmetric sulfoximine inhibitors against HIV-1 protease

“…Instead, deprotection of acetonide was observed, which is presumably due to the mesitylsulfonic acid produced in the reaction media. Non-nucleophilic base of N,N-diisopropyl-ethylamine (DI-PEA) 27 was employed in the N-methylation reaction using the Meerwein's salt to prevent the deprotection of the acid-labile acetonide groups. As expected, the crude reaction mixture of the Nmethylation reaction was directly reacted with PTSA in methanol to remove the isopropylidene and afforded the desired product 23 (Scheme 6).…”

“…General procedure for the preparation of diamide sulfoxide (27,28,29) To a solution of 24, 25, or 26 (1 equiv) in DCM (12 mL) and methanol (12 mL) at À78°C under N 2 was added mCPBA (1 equiv). The mixture was stirred at À78°C for 1 h then at room temperature for another 1 h. The reaction was quenched by diluting with DCM and extracted with saturated NaHCO 3 .…”

The Total Synthesis of the Neurogenic Ganglioside LLG‐3 Isolated from the Starfish Linckia laevigata

“…The chloroacetyl group could also be removed by using the widely used DABCO method [13] (DABCO, EtOH), however this strategy promoted the migration of the acetyl group from N5 to O8, giving the fully acetylated derivative as the major product. Removal of the chloroacetyl group using 12 and 2,6-lutidine as an acid scavenger with subsequent methylation using Meerweins reagent, [14] successfully introduced a methyl group at the C8 hydroxy group, thus generating 13 in an 81 % yield (two steps). Upon hydrogenolysis, 13 was converted into the terminal sialyl glycolic unit 14 in a quantitative yield.…”