Comparison of Bimacrocyclic, Monomacrocyclic, and Nonmacrocyclic Bis(amidomethyl)pyridines as Catalysts in the Base-Catalyzed Addition of Alcohols to Ketenes

Abstract

Nineteen new bimacrocyclic, monomacrocyclic, and nonmacrocyclic pyridines 1–6 bearing amide functions have been synthesized and utilized in base‐catalyzed additions of alcohols (ethanol, 2‐propanol) and polyols [propane‐1,2‐diol (11a), butane‐1,3‐diol (12a), methyl 4,6‐O‐benzylidene‐α‐D‐glucopyranoside (13a)] to diphenylketene. Compounds 4c, 4d and 1b proved to be efficient and selective catalysts; 4c and 4d exhibited better results with 11a and 12a, and 1b was the best catalyst for selective 2‐O‐acylation of 13a.

Acylation of 6-O-Functionalized Cellulose Ethers with Diphenylketene

“…It is known that the reactivity of diphenylketene (4) towards primary alcohols is higher than towards secondary ones. [7,9] The next step was to investigate the influence of the steric demand of the base on the acylation. Thus four pyridine bases (pyridine, 2,6-dimethylpyridine, 2,4,6-trimethylpyridine, concave base 5) differing in the shielding a Preliminary results of a methylation analysis accomplished by the group of P. Mischnick (TU Braunschweig) confirm this assumption.…”

“…[8] Diphenylketene (4) was synthesized from commercially available diphenylacetic acid (Fluka) according to the literature procedure [12] and was freshly distilled prior to use. Methyl 6-O-trityl-a-d-glucopyranoside [13] (9) and methyl 2-O-diphenylacetyl-6-O-trityl-a-d-glucopyranoside [7] (10) were prepared as described previously. Sodium hydride was prepared from its suspension in mineral oil by washing with n-pentane and drying in a flow of argon immediately before use.…”

“…Selected IR data (cm -1 ) a) 7 3 a) DS Ac was determined by quantitative IR spectroscopy. b) Despite multiple efforts to generate a pure compound, all tritylcelluloses 1 acylated in the presence of 2,6-dimethylpyridine gave poor elemental analyses.…”

“…For instance, the acylation of methyl 4,6-benzylidene-a-dglucopyranoside (3) with diphenylketene (4) as the acylating reagent and the concave base 5 as the catalyst, afforded as the only product the 2-diphenylacetyl glucoside 6 (see Figure 2). [7] Although in the acylation of the banomer, which possesses the correct configuration at the glycosidic bond, no selectivity for one of the secondary hydroxyl groups was observed with catalyst 5, interestingly a diacylated product could not be detected.…”

Concave Reagents

“…Pyridine and especially its more basic sibling DMAP [4 -(dimethylamino)pyridine] are excellent catalysts for acyl transfers. 56 More recently, concave NHC have been investigated as nucleophilic catalysts. 53 A reaction which demands less space is the formation of a hydrogen bond to the lone pair of the nitrogen, and thus catalyses via hydrogen -bond formation are easily possible with concave pyridines.…”