Carbonyl compounds 1,2-transposition

Allylsilanes react with carbonyl compounds to transfer the allyl group with 1,3-transposition, in the presence of Lewis acids, typically titanium(IV) chloride47. Recently this reaction has been carried out under super-acid catalysis48. Transfer of the allyl group is also induced by tetrabutylammonium fluoride, but in this case reaction takes place regioselectively at the less substituted end of the allyl fragment49. 

The authors of this book are not aware of any case, in which a primary allylic alcohol suffers an oxidative transposition with PCC. Such case would be most unlikely, because it would involve an equilibrating pair of allylic chromate ester, in which the less stable minor one would evolve to a carbonyl compound. 

Upon heating to 300-350 °C the ethynyl vinyl oxiranes 36, obtained by condensation of vinylsulfonium ylides with acetylenic carbonyl compounds, underwent a Cope-transposition into the oxacycloheptadiene 37, followed by a Claisen-type reaction leading to a cis, trans mixture of 2-ethynylcyclopropanecarboxaldehydes 38, Eq. (12)25). 

The oxidative rearrangement of allylic alcohols to a -unsaturated ketones or aldehydes is one of the most widely used synthetic reactions in this group, and forms part of a 1,3-carbonyl transposition sequence. Scheme 7 shows this reaction and the related conversion of the allylic alcohol to an a, -epoxy carbonyl compound. Chromate reagents induce some allylic alcohol substrates to undergo a dirMted epoxidation of the alkene without rearrangement, but this reaction is beyond the scope of the present discussion. 

The rearrangement can be catalytically brought about with silver and copper salts or mote recently with Pd compounds. a, -Unsaturated carbonyl compounds are also often formed under rearrangement on oxidation of allylic alcohols, especially when they are tertiary. This process can serve to perform a 1,3-transposition of carbonyl groups in a, -unsaturated ketones (Scheme 9). ... 

Transposition of Allylic Alcohols into Carbonyl Compounds Mediated by Transition Metal Complexes Uma, R. Crevisy, C. Gree, R. Chem. Rev. 2003,103,27. 

P-Siloxy-e-acetoxy--y,8-unsaturated carbonyl compounds undergo reductive transposition on exposure to HCOONH4, (dba)3Pd2, and BuiP in DMF to afford the 8,e-unsaturated products with (all) syn-isomers predominating.- In conjunction with the enantioselective aldol access to the substrates, this process expands the methodology of existing polyketide synthesis. 

Finally, since phenyl vinyl sulfides can be hydrolyzed to carbonyl compounds, the methodology provides a new 1,2-carbonyl transposition route. For example, 3-cholestanone... 

Trialkylstannyl-lithium reacts with secondary alkyl halides (substitution) and with a/S-unsaturated carbonyl compounds (conjugate addition) to give alkyl tin derivatives which may be oxidized with chromic anhydride in pyridine to give a saturated ketone. Applying the procedure to a cycloalkenone, an efficient dialkyl-ative enone transposition can be realized (Scheme 68). ... 

The replacement of the oxygen atom by sulfur in a Claisen rearrangement substrate brings significant differences to the process. Besides giving access to thio-carbonyl compounds, it affords a kinetically facile transposition, with a changed thermodynamic pattern (Scheme9.1). 

In 1912 Claisen described the transposition of allyl vinyl ethers to y, 8 -unsaturated carbonyl compounds under thermal conditions. - The first example of this type of [3,3 ] -sigma tropic shift performed in pure water appeared approximately 60 years later and concerned the conversion of chorismate 122 to prephenate 123 (Scheme 5.40). ... 

Two useful carbonyl group transpositions involve the intermediacy of sulphur compounds. In the first, the dithioacetal (131) is metallated (Bu"Li 4 eq.) and hydrolysed to the ketone (132), whereas Scheme 22 shows a sequence for the regiospecific transposition of cyclic conjugated enones. ... 

A regiospecific transposition of the allyl fragment involving exclusive y-reaction is observed e.g. 27 -> 28) in both studies. A related reaction between (presumably) allylic zinc derivatives and aldehydes or ketones occurs when a mixture of an allylic bromide and the carbonyl compound is passed along a column of zinc granules heated at the reflux temperature of THF. Hydrolysis of the resultant zinc alkoxide provides another route to homoallylic alcohols (Scheme 12), with no problem from Wurtz coupling of the bromide. The column may be used repeatedly without contamination, providing the zinc is replenished as it is used up. ... 

Another way to circumvent the stereoselectivity issues that may arise from olefination or addition/elimination sequences to l,4-dien-3-ones is to switch the polarity of components and olefinate a carbonyl compound with a symmetrical nucleophilic pentadienyl anion equivalent. A seminal contribution was reported by Paul and Tchelitcheff in 1951, who combined trivinylmethane (235) and carbon dioxide to form a [3]dendralene 237 (Scheme 1.40 (a)) [190]. In this instance, the anion of trivinyl methane 236 is indeed a pentadienyl anion, but bond formation occurs with allylic transposition through a vinyl unit. 

This is often achieved from 1,4-dicarbonyl compounds in a procedure similar to that used to form furans but using phosphorus pentasulfide, or Lawesson s reagent (see below), to cause a transposition from carbonyl to thiocarbonyl groups, prior to cyclization and loss of hydrogen sulfide (Scheme 6.37). 

Umezawa and co-workers9 have reported a new synthesis of the tetracyclic lactam (19), which is a key intermediate in Torssell s synthesis of lycorine (cf. Vol. 9, p. 139) the Japanese work (Scheme 2), therefore, represents a formal synthesis of the alkaloid. The cyclohexyl isocyanate (15) (trans-diequatorial aryl and isocyanate groups) cyclized to a tricyclic lactam, which by reduction with a hydride and hydrolysis gave the ketone (18). The tetracyclic ketone (16) was converted into the 2,3-ene (17) by a Cope elimination reaction, and the synthesis of compound (19) was completed by transposition of the lactam carbonyl group from C-5 to C-7. 

In 1,2-alkylative carbonyl transpositions where the carbonyl group moves forward into the newly added fragement, e. g. 63 - 64, the reagent behaves as an acyl anion equivalent. We have seen one example of this in the synthesis of the occidentalol intermediate 8. Phosphine oxides with OR or SR substituents on the a-carbon 65 are ideal reagents for this process as the Horner-Wittig reaction gives vinyl compounds which can be hydrolysed to 64. 

The a-alkylation of sulfonylhydrazone dianions with disulfides followed by Shapiro reaction has been used to effect the 1,2-transposition of carbonyl groups.19,20 As shown below, treatment of tosylhydrazone 31 with n-BuLi/TMEDA followed by addition of dimethyl disulfide and deprotonation with an additional equivalent of w-BuLi provided vinylsulfide 32.19 Exposure of this compound to mercuric chloride in hot aqueous acetonitrile provided ketone 33 in 75% overall yield. 

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