Aluminum amalgam sulfones

That propargylic starting materials are often employed in modern allene hydrocarbon chemistry is not surprising and the following examples are just a small selection from a much larger synthetic effort. Thus, the sulfones 61 are first cleaved in an aluminum amalgam-mediated reduction to the intermediates 62, which lose sulfur dioxide under the reaction conditions and furnish the trisubstituted allenes 63 in good to excellent yields (75-95%) (Scheme 5.7) [18]. 

Reductions with aluminum are carried out almost exclusively with aluminum amalgam. This is prepared by immersing strips of a thin aluminum foil in a 2% aqueous solution of mercuric chloride for 15-60 seconds, decanting the solution, rinsing the strips with absolute ethanol, then with ether, and cutting them with scissors into pieces of approximately 1 cm [141,142]. In aqueous and non-polar solvents aluminum amalgam reduces cumulative double bonds [143], ketones to pinacols [144], halogen compounds [145], nitro compounds [146, 147], azo compounds [148], azides [149], oximes [150] and quinones [151], and cleaves sulfones [141, 152, 153] and phenylhydrazones [154] (Procedure 30, p. 212). 

Vinyl fluorides,1 Fluoro(phenylsulfonyl)methylithium (2), obtained by reaction of 1 with BuLi in THF at — 78°, reacts with carbonyl compounds to form fluorohydrins (3), which are dehydrated to (E)-a-fluoro-a,p-unsaturated sulfones (4) in 67-92% yield with CH3S02C1 or orthophosphoric acid. Conversion of 4 into vinyl fluorides (5) is effected with aluminum amalgam (—90% yield). The vinyl fluorides are obtained as a 1 1 mixture of (E)- and (Z)-isomers. 

Bissulfone 11 is reduced with aluminum amalgam to sulfone 32 lipimers are obtained at this stage, which are transformed into the common product 1 through subsequent oxidation to a ketone. 

Allyl phosphates, 506 Allylsilanes, 43, 71-72, 529, 575 Allyl sulfones, 512 Allyltitaniiun ate complexes, 376-377 Allyltri-n-butyltin, 15-16 Allyltrimethylsilane, 16-20, 532 Allyltrimethyltin, 20-21 Almusone, 51 Alpine Boranc, 429 Alumina, 22-24 Aluminum amalgam, 24-25 Aluminum ate complexes, 17 Aluminum chloride, 25-28, 100 Aluminum chloride-ethanethiol, 28-29 Aluminum isopropoxide, 29, 296 Amidoalkylation, 16-17 Amidomercuration, 317 Animation, 221 Amino acid esters, 360... 

Reductive desulfurization of 9-(phenylsulfonyl)furo[2,3- ]quinoline and its 2-methyl derivative can be effected by treatment with LAH in THF solution at reflux, but proceeded poorly with aluminum amalgam, the reagent of choice for the reductive cleavage of vinyl sulfones <83JOC774>. Raney nickel was used to remove a thiomethyl substituent from the central ring of a furochromone direct precursor to visnagan <89JOC448l>. 

Vinylic sulfoxide (30) is desulfurized to (31) with f-butyllithium (equation 80), and sulfone (32) affords triphenylethylene on reduction with aluminum amalgam or lithium aluminum hydride (equation 81). ... 

Sulfinyl and sulfonyl groups are easier to reduce than a-(aikylthio)carbonyl compounds. Aluminum amalgam has frequently been used for removal of sulfinyl and sulfonyl groups. This reagent is typically used in refluxing (wet) THF reduction of 3-keto sulfones can be carried out at room temperature by Na(Hg)x, if the solution is buffered with Na2HP04 ... 

The reductive desulfonylation of vinylic sulfones has been mainly carried out with sodium and aluminum amalgams, Sml2, and Mg in M,Al-dimethyl-formamide (DMF) in the presence of chlorotrimethylsilane (TMSC1). The configuration of the double bond is not necessarily preserved in the desulfonylation of vinylic sulfones when Na/Hg is employed. This reagent is the most widely used when there is no need for stereochemical control as shown in Eqs. 2139 and 22.40... 

Zinc dust-acetic acid cleavage of a sulfone [1278. after ref. 19a]. The a-aroyl sulfone is cleaved by zinc and acetic acid in better yield than by aluminum amalgam... 

Chirality may be introduced in another part of the molecule Isobe and coworkers have performed the addition of organometallic reagents to chiral sulfones 7.78 [ 73], After sequential treatment of the adducts with tetrabutylammonium fluoride, aluminum amalgam and HgC, a-branched aldehydes were isolated with a high enantiomeric excess (Figure 7.54). Analogs formed from (5)-valinol have been used for similar purposes, but preparation of the substrates requires tedious purification [325],... 

Aluminum amalgam (Al/Hg) is also a useful reagent that is most commonly employed for hydrogenolysis of sulfur compounds.533 Reduction of sulfoxides is an important application,534 as is reduction of sulfones. Aluminum amalgam reduces the a-phenylsulfonyl moiety in 554 to give lactone 555 in 68% yield.535 Aluminum amalgam has also been used for reduction of nitro compounds to the amine,536 and reduction of azides to the amine.532... 

Segment C (21) is a relatively small molecule and is synthesized from 8. Acyclic stereocontrol for the construction of the C-29 chiral center was very important. Compound 8 was first converted to the lactone (22), which was treated with the carbanion of 23 to give 24. Removal of the sulfone with aluminum amalgam, spiro-ketalization, and Peterson olefination gave 25, which was treated with methyllithium at - 78 °C in tetrahydrofuran. Syn-addition controlled by an a-chelation occurred smoothly to give the expected segment C (21) in high yield [8a, b]. 

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