Ketones reaction with allenes

Selective 1,4-reduction of unsaturated aldehydes and ketones by 6 occurs smoothly in THF between —25 °C and room temperature within a few hours (Eq. 5.7). Particularly noteworthy is the realization that phosphines are noticeably absent from the reaction medium. The analogous combination of CuCl/BusSnH in N-methyl-2-pyrrolidinone (NMP) or DMF does not behave identically [22], failing to react with the hindered substrate isophorone, whereas a 72% yield of the corresponding reduced ketone is formed with reagents XCu(H)Li/Bu3SnH. Nonetheless, a form of CuH is being generated in this more polar medium, effectively utilized by Tanaka to arrive at 3-norcephalosporin 8 upon reaction with allenic ester 7 (Scheme 5.3). 

The reaction of salicylaldehydes with a,P-unsaturated compounds which can lead to chromenes, chromans and other heterocycles has been reviewed <07OBC1499> and details of their reaction with allenic esters and ketones have been published <07CEJ3701>. A proline-catalysed benzoic acid-promoted asymmetric synthesis of chromene-3-carbaldehydes involves a domino oxa-Michael - aldol reaction with a,P-unsaturated aldehydes the ee range is 83-98% (Scheme 11) <07CEJ574>. 

Reaction with Allenes. A diallene, hexatetraene (eq 32), reacts with Fe(CO)5 with insertion of carbon monoxide to form 2,5-dimethylenecyclopent-3-enone. Allenyl ketones, on the other hand, form dinuclear complexes. ... 

Aldehydes and ketones can be converted into terminal allenes by reaction with a-lithiovinylsilanes followed by elimination (9). 

Acylzirconocene chlorides 78, which are easily available through the hydrozirco-nation of alkenes or alkynes with Cp2Zr(H)Cl and subsequent CO insertion, can be used as acyl anion equivalents Cu(I)-catalyzed reactions with propargyl compounds 77 afford allenyl ketones 79 (Scheme 3.40) [86]. The use of an excess of 77 (2 equiv. to 78) is important for the selective preparation of 79, which prevents an undesirable side reaction of the allenic products 79 with 78. 

Buynak et al. reported the synthesis of representative 7-vinylidenecephalosporine derivatives bearing an axial allene chirality (Scheme 4.5) [9]. A chiral allene 24 was prepared stereoselectively utilizing the reaction of an organocopper reagent with propargyl triflate 23, obtained by a diastereoselective ethynylation of the ketone 22 with ethynylmagnesium bromide. Terminally unsubstituted allene 26 was synthesized via bromination of the triflate 23 followed by reduction of the bromide 25 with a zinc-copper couple. 

Several trivial but highly useful reactions are known to convert one acceptor-substituted allene into another. For example, the transformation of allenic carboxylic acids is possible both via the corresponding 2,3-allenoyl chlorides or directly to 2,3-allen-amides [182,185], Allenylimines were prepared by condensation of allenyl aldehydes with primary amines [199]. However, the analogous reaction of allenyl ketones fails because in this case the nucleophilic addition to the central carbon atom of the allenic unit predominates (cf. Section 7.3.1). Allenyl sulfoxides can be oxidized by m-CPBA to give nearly quantitatively the corresponding allenyl sulfones [200]. The reaction of the ketone 144 with bromine yields first a 2 1 mixture of the addition product 145 and the allene 146, respectively (Scheme 7.24). By use of triethylamine, the unitary product 146 is obtained [59]. The allenylphosphane oxides and allene-... 

Allenic ketones undergo a thermal cycloaddition reaction with 1,3-dienes. The carbon-carbon double bond proximal to the carbonyl group reacts exclusively as in the case of allenic esters [105]. 

Table 12.7 Reactions of cyclic dienes with allenic ketones.

The addition of allenyl ether-derived anions to Weinreb [4] or to morpholino amides [5] follows a slightly different pathway (Eq. 13.2). For example, the addition of lithioallene 6 to Weinreb amide 7 at -78 °C, followed by quenching the reaction with aqueous NaH2P04 and allowing the mixture to warm to room temperature leads to cyclopentenone 9 in 80% yield [6]. The presumed intermediate of this reaction, allenyl vinyl ketone 8, was not isolated, as it underwent cyclization to 9 spontaneously [7]. These are exceptionally mild conditions for a Nazarov reaction and are probably a reflection of the strain that is present in the allene function, and also the low barrier for approach of the sp and sp2 carbon atoms. What is also noteworthy is the marked kinetic preference for the formation of the Z-isomer of the exocyclic double bond in 9. Had the Nazarov cyclization of 8 been conducted with catalysis by strong acid, it is unlikely that the kinetic product would have been observed. 

An interesting novel coupling reaction of allenes with carbonyl compounds mediated by a lanthanide metal species was reported recently [80], The samarium(II) iodide-mediated reaction of various ketones or aldehydes 153 with methoxyallene (56) afforded exclusively y-addition products 4-hydroxy-l-enol ethers 154 in moderate to good yields with low cis/trans selectivity (Scheme 14.39). 

The reaction of allenes with peracids and other oxygen transfer reagents such as dimethyldioxirane (DM DO) or hydrogen peroxide proceeds via allene oxide intermediates (Scheme 17.17). The allene oxide moiety is a versatile functionality. It encompasses the structural features of an epoxide, an olefin and an enol ether. These reactive intermediates may then isomerize to cyclopropanones, react with nucleophiles to give functionalized ketones or participate in a second epoxidation reaction to give spirodioxides, which can react further with a nucleophile to give hydroxy ketones. 

Treatment of the acetylenic ketones 186 with lithium dialkylcuprates and trapping the resultant enolates with acetic anhydride produced the enyne-allene 187 (Scheme 20.39) [72], Regeneration of the oxyanion-substituted enyne-allene system using methyllithium at -20 °C led to the formation of either the indanones 188 or the ben-zofluorenones 189 through a Schmittel cyclization reaction. 

Lithio-l-methoxyallene 183 ° , readily accessible by deprotonation of methoxyal-lene with n-butyllithium in diethyl ether, turned out to be a versatile C-3 building blocL It adds to aldehydes and ketones giving hydroxyaUcylated allenes 184, which undergo a ring-closure reaction under basic conditions. Thus, 3-methoxy-2,5-dihydrofurans 185 are obtained. Subsequent acid hydrolysis leads to the formation of dihydro-3(2//)-... 

Complexes involving oxime ligands display a variety of reactivity modes that lead to unusual types of chemical compounds. As far as the oxime chemistry of platinum is concerned, these complexes are involved in facile deprotonation of the OH group with formation of oximato complexes, reduction of Pt(IV) species, Pt(II)-assisted reactions with coordinated allene," alkylation by ketones, oxime-ligand-supported stabilization of Pt(III)—Pt(III) compounds, oxidative conversion into rare nitrosoalkane platinum(II) species, and coupling with organocyanamides. ... 

It is reported that the palladium-catalysed intramolecular aromatization of 1,1 -dichloro-9/T-fluoren-9-yIidene (15) may lead to the formation of fullerene fragments.89 The amiulation reaction, under palladium catalysis, between iodoanflines and ketones may yield indole derivatives.90 There have also been studies of the palladium-catalysed carbonylation of o-iodophenols with allenes which may lead to l-benzopyran-4-one derivatives,91 of the intramolecular coupling of phenols with aryl halides,92 and of the intramolecular Heck aiylation of cyclic enamides.93... 

The first cyclopropanone to be isolated under Favorskii conditions was obtained from the reaction of the sterically hindered a-bromodineo-pentyl ketone (57) with potassium >-chlorophenyl-dimethylcarbinolate.13> The product, 7f MS-2,3-di-f-butylcyclopropanone (52) (20—40%) was later prepared independently by the valence isomerism of l,3-di-7-butyl-allene oxide 51> (see Section 2.6). 

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