Base induced elimination sulfones

The reaction of 3-methoxy-1,2,4-triazine 1-oxide 20 with the carbanion generated from chloromethyl phenyl sulfone proceeds as the vicarious nucleophilic substitution (VNS) of hydrogen (Scheme 1, path B) via addition of the carbanion at position 5 of the heterocycle. Following base-induced elimination of HCl and protonation, 3-methoxy-5-phenylsulfonyl-1,2,4-triazine 4-oxides 65 result (88LA627). 

Base-induced eliminative ring fission, in which both the double bond and the sulfone function take part, has been observed in thiete dioxides253. The reaction can be rationalized in terms of initial Michael-type addition to the double bond of the ring vinyl sulfone, followed by a reverse aldol condensation with ring opening. The isolation of the ether 270c in the treatment of 6c with potassium ethoxide (since the transformation 267 -> 268 is not possible in this case) is in agreement with the reaction mechanism outlined in equation 101253. 

These are good dienophiles. and aryl vinyl sulfones have found use as equivalents of ethylene and ketene through functional modifications of their adducts. However, as the base-induced elimination of a sulfinic acid to yield an olefin occurs only with difficulty, they are not direct precursors of acetylene equivalents, unless suitably modified as in ( )-l-phenyl-sulfonyl-2-trimethylsilyl ethylene (PhS02-CH=CH-TMS). In its cycloadducts the elimination to an alkene is smoothly realized by the fluoride ion. If an alkylation step is previously carried out on the adduct, the overall process realizes an indirect addition of a terminal acetylene, as in the examples given here [533]. 

Easily available anomeric sulfones, which have already been mentioned as glycal precursors, readily undergo base-induced eliminations resulting in formation of 1,2-unsaturated p)ra-nose derivatives in which the sulfonyl group has been retained [150,151]. Such compounds have considerable synthetic potential, particularly for C-C bond formation. For example, compound 49 can be lithiated with LDA/THF at 80 °C to afford C-2 branched glycals 50 (O Scheme 16) [152]. 

The synthesis of stereodefined acyclic alkenes via 3-elimination reactions—such as (1) dehydration of alcohols, (2) base-induced eliminations of alkyl halides or sulfonates (tosyl or mesyl esters), and (3) Hofmann eliminations of quaternary ammonium salts—often suffers from a lack of regio- and stereoselectivity, producing mixtures of isomeric alkenes. 

A number of alkenyl- and alkylidenecyclopropanes have been made by base-induced eliminations of sulfonates. The first of these was the preparation of bicyclopropylidene (3) from the corresponding tosylate 2. Efficient syntheses of 3 via 1-cyclopropylcyclopropanol (1) and the corresponding chloride or bromide have been presented (see Section 5.2.2.I.I.2.). An alternative method is to convert alcohol 1 to the tosylate 2 and to treat the latter with potassium /ert-butoxide in dimethyl sulfoxide. This procedure had been reported to yield better than 50% of bicyclopropylidene based on the alcohol, but this has been found to be difficult to reproduce. The best method for the preparation of 3 has been determined to be via 1-bromo-l-cyclopropylcyclopropane by dehydrobromination (see Section 5.2.2.1.1.2.). 

Cyclopentene derivatives with unsaturated appendages are also available via this general annulation strategy representative examples are presented in Scheme 15. In these several transformations desulfonylation is achieved using base-induced -elimination, via the fluoride-promoted elimination of 3-silyl sulfones, and by means of Brook rearrangement chemistry according to the method of Reich. In summary, a wide variety of complex functionalized cyclopentenes are available using this versatile [4 1]... 

In a so-called vicarious nucleophilic substitution of hydrogen, the carbanion of an arene halomethyl sulfone adds to the electron-deficient ring position of nitroarenes or azaaromatic systems such as quinoxalines and naphthyridines, followed by base-induced /(-elimination of the corresponding hydrogen halide.73... 

One of the most commoidy used methods for forming carbon-carbon double bonds is by -elimination reactions of the types shown in Scheme 2.1, where X = e.g. OH, OCOR, halogen, OSO2R, NRa, etc. Included among these reactions are acid-catalysed dehydrations of alcohols, solvolytic and base-induced eliminations from alkyl halides or sulfonates and the Hofmann elimination from quaternary ammonium salts. They proceed by both E2 (elimination bimolecular) and E1 (elimination... 

In spite of the disadvantages, acid-catalysed dehydration of alcohols and base-induced eliminations from halides and sulfonates are used widely in the preparation of alkenes. Typical bases include alkali-metal hydroxides and alkoxides,... 

The Julia olefination allows the generation of a double bond by alkylation of a suUbne, followed by a base-induced elimination of ben-zenesulfinic add. The water-soluble sulfinate can be separated off, and recovered as the free sulfinic add. The sulfone is then obtained by reaction ofthe sulfinic acid with the appropriate alkyl halide. [73]... 

The protocol consisting of alkylation followed by oxidation and base-induced elimination of sulfones can also be found in the strategy of other solid phase syntheses. Lam et al. for example constructed o ,)S-unsaturated ketones 475, [291] as well as various heterocyclic compounds 469-474 and 476-478 following this route. Scheme 71 gives an overview of possible structures obtainable from sulfone-linked y6-carbonyl compounds 468a,b. 

A traceless linker for anchoring secondary amines has been developed [123,124] and is referred to as the REM linker 21 (regenerated after cleavage, functionalized by Michael addition). Tertiary amines can be prepared on this support by conversion to a resin-bound quaternary ammonium salt followed by cleavage by base-induced Hofmann elimination [125]. The analogous vinyl sulfone resin 2m can also be used to anchor secondary amines and is stable to a greater range of reactants [126,127]. 

The tosylation of carbon can be accomplished using electron transfer conditions. Treatment of styrene and analogs with Copper(II) Chloride and tosyl chloride or Benzenesulfonyl Chloride results in a formal replacement of the vinyl proton by the sulfonyl moiety (eq 35). The intermediacy of a trans-(S-chloro sulfone has been demonstrated by H NMR. Treatment with base induced the elimination of HCl. A variety of other sulfonyl transfer reagents can be ertployed in the synthesis of isolated /3-chloro sulfones, with good results (60-97% yield) for a variety of alkenes (ethylene, 1-butene, 2-butene, 1-octene, acrylonitrile, methyl acrylate, and 1,3-butadiene). ... 

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