[15590-26-8] · C2H5KOS · Potassium Methylsulfinylmethylide · (MW 116.24)
(a strong base and nucleophile, very useful for the introduction of the methylsulfinylmethyl group1)
Alternate Name: potassium dimsylate; dimsylpotassium; KDMSO.
Form Supplied in: not commercially available.
Preparative Methods: prepared by the reaction of Potassium Amide or Potassium Hydride with Dimethyl Sulfoxide (DMSO).3,4 Equilibrium quantities of KDMSO may be prepared using Potassium t-Butoxide in DMSO.5
Handling, Storage, and Precautions: best prepared as needed although synthesis and storage procedures similar to those used in some preparations of Sodium Methylsulfinylmethylide (NaDMSO) would probably result in long shelf life.6 Hydrogen gas may be emitted during the preparation of this reagent and due caution should be exercised in its preparation, particularly on a large scale. Problems encountered in the preparation of NaDMSO may be relevant to KDMSO.7
The conjugate base of dimethyl sulfoxide (pK
It should be noted that the generation of KDMSO with t-BuOK in DMSO results in the formation of only equilibrium amounts of carbanion. While this is sufficient to make products derived from KDMSO attack preponderant in many instances (e.g. nucleophilic addition), when this combination is used for its basic properties it is likely that the active agent is t-BuOK and not KDMSO.8
KDMSO has been used to conjugate dienes in natural oils such as linseed oils.9 KDMSO works much better than NaDMSO in facilitating this reaction. This isomerization procedure has also been used with synthetic compounds (eq 1).10
In work involving the nature of stabilizing effects in dianions it has been demonstrated that in the presence of excess KDMSO, 2-(diphenylmethyl)-1,1,3,3-tetraphenylpropene can be deprotonated to a dianion which is
y-aromatic (eq 2).11
Elimination reactions allegedly using KDMSO probably involve t-BuOK when the latter is used to generate KDMSO in DMSO.8 Such eliminations are not covered here. There are bona fide examples of eliminations using KDMSO produced stoichiometrically.
For example, as part of a total synthesis of elfamycin, treatment of bis-epoxide (1) gave the tetrahydrofuran (2) in a tandem elimination-ring closure sequence (eq 3).12
A new, general synthesis of ortho-alkenyl anilines is based on an elimination reaction of benzothiazines to give sulfinanilides in high yield (eq 4).13 The latter are easily hydrolyzed to free anilines.
The exhaustive O-alkylation of oligo- and polysaccharides (Hokomori reaction) greatly facilitates the handling and analysis of such compounds. The use of KDMSO as a base in this application of the Williamson ether synthesis and its superiority over NaDMSO have been documented.14
The reaction of dimsyl anions with esters leads generally to b-keto sulfoxides. KDMSO generated from t-BuOK in DMSO has been used for this purpose (eq 5).15 The importance of this reaction lies in the synthetic utility of b-keto sulfoxides.16 For example, they are readily and regioselectively alkylated and desulfurized to give ketones (eq 6) and, inter alia, can be converted to a-keto aldehydes (eq 7).15
KDMSO derived from t-BuOK in DMSO reacts with aromatic aldehydes to give the expected products.5 Interestingly, at higher temperatures and in the presence of diphenylmethane, a series of transformations takes place which result in the formation of an alkene containing no sulfur, but including a molecule of diphenylmethane (eq 8).17
Even more interesting is the report of diene diol formation from an epoxy ketone (eq 9).18 A related reaction may be taking place in the conversion of cyclohexanone to 2-methylenecyclohexanol (eq 10).19
Dimsyl anions do undergo additions to Michael acceptors, even those which are not very activated. Two examples using KDMSO are illustrative of the diverse types of alkenes which can be expected to be subject to nucleophilic attack using KDMSO (eqs 11 and 12).10,20 Cyclopropane formation, though potentially useful, is probably better accomplished using sulfur ylides or related compounds.
University of Missouri-Columbia, MO, USA