Acylation Mechanisms of DMSO/[D₆]DMSO with Di‐tert‐butylketene and Its Congeners

Abstract

Dimethyl sulfoxide (DMSO) and tBu 2 C=C=O in diglyme require heating to about 150°C to furnish the Pummerer-type product tBu 2 CHCO 2 CH 2 SCH 3 through a novel mechanistic variant. The "ester enolate" tBu 2 C=C(O -)-O-S + (CH 3 ) 2 arising through the reversible addition of DMSO (step 1) to C-1 of tBu 2 C=C=O must be trapped through protonation (step 2) at C-2 by a carboxylic acid catalyst to form tBu 2 CH-C(=O)-O-S + (CH 3 ) 2 so that the reaction can proceed. The ensuing cleavage (step 3) of the O-S bond and one of the C-H bonds in the -S(CH 3 ) 2 group (E2 elimination, no ylide intermediate) results in the formation of tBu 2 CHCO 2 -and H 3 CS-CH 2 + , whose combination (step 4) generates the final product. With a mixture of DMSO and [D 6 ]DMSO competing for tBu 2 C=C=O in diglyme, the small value of the kinetic H/D isotope effect (KIE) k H /k D = 1.26 at 150°C indicates that the cleavage of the C-H/C-D bonds (step 3) does not occur in the transition state with the highest free enthalpy. Therefore, the practically isotope-independent steps 1 and 2 determine

From organocatalysed desilylations to high-yielding benzylidenations of electron-deficient benzaldehydes

“…Previously our group has employed TCT/DMSO in several organic transformations, including selective chlorinations, 15 etherifications, 16 the methylene acetalation of alcohols 17 and the synthesis of methylenebisamides from amides. 18 Based on this research and other related reports, [19][20][21] it was speculated that the precatalyst here is chloromethyl methyl sulfide (MeSCH 2 Cl). Therefore, chloromethyl methyl sulfide was prepared using TCT and DMSO, 22 and then used in the desilylation reactions.…”

“…Research on its further applications is underway in our group. Experimental 1 H NMR, 13 C NMR and 19 F NMR spectra were recorded with a Bruker AM400, 400 MHz spectrometer using TMS as an internal standard and CF 3 COOH as an external standard for 19 F NMR. Multiplicities are reported as follows: singlet (s), broad singlet (bs), doublet (d), triplet (t), quartet (q), multiplet (m) and dd (doublet of doublets).…”

Practical Glucosylations and Mannosylations Using Anomeric Benzoyloxy as a Leaving Group Activated by Sulfonium Ion

“…This compound was also reported by Knorr in the reaction between acyl chloride and DMSO. 42 On the basis of this, a mixture of 1a and 2a (1.0 equiv each) was treated with MeSCH 2 Cl (2.5 equiv) and KI (0.7 equiv) in MeCN (2 mL) at room temperature and at 45 °C, but no glycosylations occurred ( Table 1 , entries 1 and 2). However, to our delight, elevating the temperature to 80 °C produced 3a in 35% yield ( Table 1 , entry 3), and increasing the amount of glycosyl ester to 1.9 equiv raised the yield to 46% ( Table 1 , entry 4).…”

Carbenoid-mediated nucleophilic “hydrolysis” of 2-(dichloromethylidene)-1,1,3,3-tetramethylindane with DMSO participation, affording access to one-sidedly overcrowded ketone and bromoalkene descendants§

“…In a rapid oxygen-transfer reaction that is known [ 31 – 32 ] for saturated carbenes or carbenoids, 12 will attack the solvent DMSO to generate the K,O-carbenoid 15 which decays in an E1cb-like expulsion of the observed Me 2 S. The resultant, still unknown di- tert -alkyl ketene 18 appears to have only limited options in this milieu: Taking t- Bu 2 C=C=O [ 2 ] as a model of the slightly less congested ketene 18 , a Pummerer-type acylation of DMSO by 18 should require the assistance of a carboxylic acid [ 33 ]; this is excluded in our strongly basic system. On the other hand, KOH consumed t- Bu 2 C=C=O at rt readily [ 34 ]; thus, the certainly faster addition of KOH to 18 can give the observed (in situ 1 H NMR) potassium salt 17 of 10 .…”