Methylenation sulfur stabilized

Most of the applications of sulfoxides in synthesis make use of the reactions of sulfur-stabilized carbanions with electrophiles [385, 386]. Thus the methylsulfinyl methylene carbanion, conveniently generated through the interaction of sodium hydride with DMSO [387], is a powerful nucleophile. 

SULFUR-STABILIZED METHYLENATION THE JOHNSON (N-METHYLPHENYLSULFONIMIDOYL)METHYLLITHIUM METHOD... 

Another variation of this ring expansion used sulfur stabilized cations. When aldehyde 65 was treated with trimethylsilyl methyl sulfide and trimethylsilyl triflate, cation 66 was formed and rearranged to the more stable tertiary cation 67. Elimination of the silyl group gave a 59% yield of the ejco-methylene derivative (68). 9... 

The stereoselective synthesis of bakkenolide-A illustrates a novel lactone spiroannelation reaction based on [2,3]sigmatropic rearrangement of nucleophilic carbenes. The desired sulfur-stabilized carbene (A) has been generated by a Bamford-Stevens reaction, and readily undergoes rearrangement across the less sterically biased convex face of the molecule, establishing the asymmetric center at C-7 and the necessary functionality for further elaboration of the jS-methylene-y-butyrolactone ring. 

The bulk of 4-methylphenol is used in the production of phenoHc antioxidants. The alkylation of 4-methylphenol with isobutylene under acid catalysis yields 2-/ f2 -butyl-4-methylphenol [2409-55-4] and 2,6-di-/ f2 -butyl-4-methylphenol [128-37-0]. The former condenses with formaldehyde under acid catalysis to yield 2,2 -methylene bis(6-/ f2 -butyl-4-methylphenol) [119-47-1], which is widely used in the stabilization of natural and synthetic mbber (43). The reaction of 2-/ l -butyl-4-methylphenol with sulfur dichloride yields 2,2 -thiobis(6-/ l -butyl-4-methylphenol) [90-66-4]. 

The substitution of a heteroatom for an a-sulfoxy methylene group substantially increases the preference for an axial orientation of the sulfoxide oxygen320, despite the smaller space requirement of the sulfur with its lone pairs, compared to that of a methylene group321, at least in the case of 1,3-dithiolane oxides. The substituting heteroatom, therefore, should decrease the conformation stability (i.e. lower the barrier to chair-chair interconversion). 

Method 4(when acardite II alone is present as stabilizer and gelatinizer) a)Extract a finely divided sample of propellant(ca lOg) with methylene chloride or chlf and evap the solvent b) Dry at 110° and weigh(wt 1) (acardite II is not volatile at 110°) c)Det the mp and if it is ca 170.5°, the identity of acardite II is established. If mp differs from 170.5°, boil the residue with ethanol and aq sulfuric acid to split the acardite II ... 

Recently, Agasti et al.158 studied the thermodynamic and kinetic stability of MPCs that differ in the substitution pattern on the first and second carbon next to the sulfur atom (Fig. 4.5). The rate constant of the decomposition of MPCs by potassium cyanide increases in the series iso-thiolate (a methyl group on C2) < nor-thiolate (two methylene groups next to S) < sec-thiolate (a methyl group on Cl). Moreover,... 

The dehydrogenation of bis(a-bromobenzyl) sulfide (41) with Fe2(CO)9 in the presence of furan affords (43). The iron-stabilized sulfur ylide (42) has been proposed as intermediate. Reaction of C -di-phenylnitrone (44) with l,2-bis(methylene)-3,3.4,4,5,5-hexamethylcyclopentane (45) in benzene at 80 C gives a [4 -I- 3] cycloadduct (46 18%), along with some other products. Landor et al. have shown that the dehydrobromination of allenyl bromide (47) in the presence of furan affords bicyclic ketone (49) in 9% yield. Apparently, a strain alkyne intermediate reacts with r-butyl alcohol to afford an enol ether (48), which is then converted to (49) (Scheme 11). 

The ability of sulfur to stabilize carbanions is exemplified in the following cases. The pentadienyldi-thiocarbamate (144 Scheme 11) can be alkylated at the methylene group to afford the methylated product (145). At 110 C, the dithiocarbamate unit walks its way to the other end of the pentadienyl chain via tandem [3,3] sigmatropic rearrangements. The formation of (14d) is thermodynamically controlled as the more-substituted pentadienyl unit is formed. Dithiocarbamate (146) can be alkylated and eventually transformed into sulfur-free products the sequence giving (148) from (146) is but one of these processes. 

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