Carbonylation of Allenes

This chapter deals with an overview of the catalytic carbonylation procedures of allenes with carbon monoxide for organic synthesis. 

Modem Carbonylation Methods. Edited by Laszlo Kollir 

Copyright 2008 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim 

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Carbonylation of the complex 548 proceeds in ethanol gives ethyl 3-chloro-3-butenoate (554), The lactone 555 and the two esters 556 and 557 are obtained by carbonylation of the dimeric complex 549. The oxidative carbonylation of allene in ethanol with PdCl2 gives ethyl itacoante (558), although the yield is low[498]. 

The catalytic oxidative carbonylation of allene with PdCb and CuCh in MeOH affords methyl a-methoxymethacrylate (559)[499]. The intramolecular oxidative aminocarbonylation of the 6-aminoallene 560 affords the unsaturated J-amino ester 561. The reaction has been applied to the enantioselective synthesis of pumiliotoxin (562)[500]. A similar intramolecular oxycarbonyla-tion of 6-hydroxyallenes affords 2-(2-tetrahydrofuranyl)acrylates[501]. 

The PTC reaction of fulvenes with CO/Mel gives monoacylated derivatives as the major products [155]. Metal-carbonyl catalyzed reactions of allenes have also been affected under PTC conditions (eq. (14)). Nickel cyanide catalyzes the re-giospecific carbonylation of allenes to y9,y-unsaturated acids [ 156] while hydroxy-ketones are usually the main products when Co2(CO)g and Mel are used [157]. The PTC reaction of allenes with CO in the presence of Mn2(CO)io and Mel afford (Z)-a,y5-unsaturated ketones [158]. 

Few studies on Pd-catalyzed carbonylation of allenes have been reported. Grigg carried out the carbonylation of allene in the presence of phenol under 1 atm at 100 °C and obtained phenyl methacrylate (117) by the attack of the central carbon [36], Carbonylation in the presence of secondary amine and AcOH occurred at the C-2 position to give a,/I-unsaturated amides such as 118 [36]. 

This carbonylation of allenes includes the formation of vinylidenyl Jt-allylpalla-dium complexes as the key intermediate after the elimination of the carbonate group [7]. Furthermore, nine-membered cyclic compounds are prepared successfully with alkylidenyl 7t-allylpalladium complex as the key intermediate (Scheme 11.5) 8]. 

Platinum complexes also exhibit catalytic activity toward the carbonylation of allene with CO and aliphatic thiol can react with allene regioselectively [12]. The PtCl2(PPh3)2-catalyzed carbonylative thiolation of cyclohexylallene with I " Hex-SH) as an aliphatic thiol carbon monoxide by the use of aliphatic thiol ( Hex-CH) proceeds regioselectively at the terminal double bond of the allene. In the case of Pt(PPh3)4-catalyzed reaction, the thiolative carbonylation takes place at both terminal and central double bonds (Scheme 11.9). 

The catalytic carbonylation of allenes can be employed for the synthesis of heterocyclic carbonyl compounds, as shown in Scheme 11.10 [13], which may proceed through oxidative addition of -SH (not Ar-I) to Pd and the following hydropalladation of allene. 

The Ti(II)-mediated stereoselective reaction of allenyne with CO is reported to give bicyclic ketone (Scheme 11.18) [20[. The formation of the titanabicycle occurs from the less hindered side of the allene moiety, resulting in the production of bicyclic ketone stereoselectively. This reaction requires slightly excess amounts of the Ti reagent (not a catalytic reaction), but these results show the capability of stereoselective carbonylation of allenes. 

In conclusion, the carbonylation of allenes provides useful methods for the synthesis of functionalized unsaturated carbonyl compounds and cycUc carbonyl compounds. 

Kajitani M, Kamiya I, Nomoto A, KiharaN, Ogawa A. Tran-sition-metal-catalyzed carbonylation of allenes with carbon monoxide and tbiols. Tetrahedron 2006 62 6355-6360. 

Nomoto A, Ogawa A (2008) Carbonylation of Allenes. In Kollar L (ed) Modem carbonylation methods. Wiley-VCH, Weinheim... 

The formation of the naphthalene (73) from the bis-ylide (72) and diethyl ketomalonate involves an unusual olefin synthesis on the carbonyl of an ester group. The methylene-pyrans (75) were formed when the diethyl malonates (74) were refluxed with j3-keto-ylides in xylene or decalin. Possible intermediates are the ketens (76) and the allenes (77). Addition of ylide to the allenes gives the betaines (78) which form methylene-pyrans either directly or via acetylenes as shown. 

Nickel-catalyzed carbonylation of a-haloalkynes with carbon monoxide under phase-transfer conditions gave either allenic monoacids or unsaturated diacids.93 The carbonylation initially afforded monoacids, which reacted further to give diacids with high stereoselectivity (Eq. 4.52). 

A regio- and diastereoselective Pd-catalyzed domino silastannylation/allyl addition of allenes 6/1-236 containing a carbonyl moiety with Bu3Sn-SiMe3 6/1-237 is described by Kang and coworkers [117]. The reaction allows the synthesis of hetero-and carbocyclic compounds with a ring size of five and six. It can be assumed that... 

Air-stable palladium(O) catalyst, [(Cy3P)2Pd(H)(H20)]BF4, catalyses carbonylation of propargylic alcohols to generate dienoic acids and esters (equation 167)286. Since propar-gyl alcohols are obtained from carbonyl compounds by acetyhde addition reactions, this sequence constitutes a three-carbon homologation. a-Allenic alcohols are converted to tt-vinylacrylic acids under similar conditions (equation 168)287. 

Attempts to employ allenes in palladium-catalyzed oxidations have so far given dimeric products via jr al lyI complexes of type 7i62.63. The fact that only very little 1,2-addition product is formed via nucleophilic attack on jral ly I complex 69 indicates that the kinetic chloropalladation intermediate is 70. Although formation of 70 is reversible, it is trapped by the excess of allene present in the catalytic reaction to give dimeric products. The only reported example of a selective intermolecular 1,2-addition to allenes is the carbonylation given in equation 31, which is a stoichiometric oxidation64. 

An example of an intramolecular palladium-catalyzed oxidation of an allene involving carbonylation was used in the synthesis of pumilotoxin 251 D (equation 32)65. Intramolecular aminopalladation of the allene followed by carbonylation of the palladium-carbon bond and subsequent oxidative cleavage of the acylpalladium intermediate by CuCE afforded pyrrolidine 72 in which the chirality at the carbon at the 2-position was established. 

The Pd-catalysed carbonylation of alkynyl epoxides 60 and alkynyldioxolanones 61 leads to the allenes 62 which can then be converted to the same pyranones through a tandem conjugate addition-cyclisation (Scheme 40) <00JCS(P1)3188>. Carbonylation of allenyl alcohols is catalysed by Ru3(CO)i2 and yields 5,6-dihydropyran-2-ones . 

A single example of the reductive cyclization of allenic carbonyl compounds is reported, which employs a rhodium-based catalyst in conjunction with Et3SiH as terminal reductant.113 This protocol promotes hydrosilylation-cyclization to form both five- and six-membered rings with exceptional levels of yy -diastereocontrol. As revealed... 

Although detailed mechanistic studies are not reported, the postulated mechanism for the reductive cyclization of allenic carbonyl compounds involves entry into the catalytic cycle via silane oxidative addition. Allene silylrhodation then provides the cr-allylrhodium hydride A-18, which upon carbometallation of the appendant aldehyde gives rise to rhodium alkoxide B-14. Oxygen-hydrogen reductive elimination furnishes the hydrosilylation-cyclization product... 

Weinreb et al86 have also studied the participation of allenes in imino-ene and carbonyl-ene reactions. Gycloisomerization of imine 133 in the presence of stannic chloride gave exclusively the m-substituted cyclopentyl isomer 135 (Scheme 27). The thermal imino-ene reaction of 136 was equally effective. More highly substituted... 

Hydrozirconation of allenic systems preferentially leads to allylic zirconocenes, which are highly reactive and thus very useful organometallic reagents. Allenic sulfides react in the expected fashion to give the (E)-y-thiophenylallylzirconocene chloride 20 (Scheme 4.18) [47]. These intermediates, upon introduction of an aldehyde or methyl ketone, give predominantly the anti isomer (ratios from 82 18 to > 97 3). Exclusive 1,2-addition was observed by Suzuki et al. in the case of an a,f5-unsaturated aldehyde. As long as the steric demands of the two substituents attached to the ketone carbonyl are significantly different, synthetically useful levels of selectivity can be achieved. 

In 0.10 M KC1, the SERS spectra of 2 show a small band at about 1690 cm-1, attributable to the carbonyl stretch. Allen and Van Duyne (12) have considered orientational effects on band intensities and have concluded that the relative intensities should be given by Equation 2, where the intensity of the carbonyl band... 

The second large class of allenes with carbonyl groups as substituents is derivatives of carboxylic acids. Overall, the same principles as with the aldehydes and ketones apply, but not as many examples are known, which might originate in part from the lower acidity of the a-hydrogen atoms of the carbonyl group compared with aldehydes and ketones. 

The use of organotitanium compounds in the synthesis of allenes involves mainly Wittig-type olefmation reactions of carbonyl compounds [86] with titanium ylides. The formation of allenes according to the scheme Q + Q + Q was described by... 

Allenic esters can be generated by palladium-catalyzed carbonylation of propargyl compounds (see Section 7.2.6). Under the reaction conditions applied, however, succeeding reactions occur directly in many cases, for instance by introduction of a second ester function. Many examples of such carbonylation reactions of allenic esters were summarized in a review by Tsuji and Mandai [136],... 

The addition of carbonyl compounds towards lithiated 1-siloxy-substituted allenes does not proceed in the manner described above for alkoxyallenes. Tius and co-work-ers found that treatment of 1-siloxy-substituted allene 67 with tert-butyllithium and subsequent addition of aldehydes or ketones led to the formation of ,/i-unsaturated acyl silanes 70 (Scheme 8.19) [66]. This simple and convenient method starts with the usual lithiation of allene 67 at C-l but is followed by a migration of the silyl group from oxygen to C-l, thus forming the lithium enolate 69, which finally adds to the carbonyl species. Transmetalation of the lithiated intermediate 69 to the corresponding zinc enolate provided better access to acylsilanes derived from enolizable aldehydes. For reactions of 69 with ketones, transmetalation to a magnesium species seems to afford optimal results. 

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]. 

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