1,4-Diazabicyclo[2.2.2]octane (DABCO) - an Efficient Reagent in the Synthesis of Alkyl Tosylates or Sulfenates

A Radical Version of the Bromo‐ and the Iodocyclization of Bis(homoallylic) Alcohols — The Synthesis of Halogenated Tetrahydrofurans by Stereoselective Alkoxyl Radical Ring Closures

“…[27] Work up of the reaction mixture provided 981 mg (98%) of 2-(2-naphthyl)-4-penten-1-yl p-toluenesulfonate as a colorless liquid. 47.…”

“…[23] 2-, and 3-Phenylsubstituted bis(homoallylic) alcohols 1b, [25] 1c, and 1f [26] were esterified with p-toluenesulfonyl chloride in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) to furnish the corresponding tosylates (96% from 1b, 88% from 1c, and 83% from 1f, not shown in Table 1). [20,27] Treatment of these alkylating reagents with 4-(p-chlorophenyl)-Nhydroxythiazole-2(3H)-thione tetraethylammonium salt in anhydrous DMF afforded alkoxyl radical precursors 6b, 6c, and 6f [23] in 45Ϫ53% yield (entries 2, 3, 7, Table 1). N-Alkoxypyridine-2(1H)-thiones 7a, [21] 7d, and 7e were prepared by adding PPh 3 to a solution of 2,2Ј-dithiopyridine-1,1Ј-dioxide [28] and a benzylic alkenol (i.e.…”

Synthesis of enantiopure (2R)-configured muscarine alkaloids via selective alkoxyl radical ring-closure reactions

“…of diisobutylaluminum hydride (DIBAH) in hexane/Et 2 O and subsequently with allyl magnesium bromide in Et 2 O (both steps at −78°C) to furnish 2-tetrahydropyranyloxy-5-hexen-3-ol 3 as a mixture of diastereomers (69% starting from 2, Scheme 1). O-Acylation of compound 3 was achieved with a mixture of 1,4-diazabicyclo-[2.2.2]octane (DABCO) 19 and benzoyl chloride in CH 2 Cl 2 (82%). This step was followed by removal of the THP protecting group under acidic conditions 20 to yield a 54:46 mixture of 3-benzoyloxy-5-hexen-2-ols 4 and 5.…”

“…Separation of this mixture into equal amounts of (2S,3S)-configured alkenol 4 and its (2S,3R)-stereoisomer 5 was accomplished on a preparative scale by HPLC (4:5=50:50). Both purified products 4 and 5 were esterified with the combination of p-toluenesulfonyl chloride and DABCO 19 in dry CH 2 Cl 2 (94% for both transformations, not shown in Scheme 1) followed by treatment with N-hydroxy-4-methylthiazole-2(3H)thione tetraethylammonium salt 21 in anhydrous DMF to provide 83% of (2R,3S)-N-(3-benzoyloxy-5-hexen-2-oxy)thiazolethione 6 and 73% of its (2R,3R)-diastereomer 7, respectively both as tan oils.…”

An Efficient One-Pot Conversion of THP- and TMS Ethers to Sulfonate Esters Using FeCl3-Montmorillonite K-10 Clay

“…p-Toluenesulfonate-and methanesulfonate esters are the most frequently used groups for preparative work. The usual method for preparation of sulfonates relies on the use of the corresponding sulfonyl chloride or anhydride in the presence of triethylamine [1], pyridine [2], 1,4-diazabicyclo[2.2.2]octane (DABCO) [3] or aqueous base in a Schotten-Baumann type reaction. An alternative for preparing tosylates and mesylates is to convert the alcohol into its lithium salt, which is then allowed to react with the sulfonyl chloride [4].…”