Aldehydes, allenylation

Arylative or silylative cyclizations of allenyl aldehydes or ketones have been reported (Equations (101) and (102)).459,459a The intermolecular process, that is, three-component coupling reaction of aldehydes, allenes, and arylboronic acids, is catalyzed by palladium as well (Equation (103)).46O 46Oa These reactions are proposed to proceed through nucleophilic attack of the allylpalladium intermediates to the carbonyl groups. 

Using allyl alcohol as an olefinic reagent, the allenyl aldehyde 37 was formed by the elimination of a /3-hydrogen atom which is adjacent to the -OH group in the intermediate 36 (Scheme 3.20) [54]. 

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-... 

When allenyl aldehydes are allowed to react with DMDO, the aldehyde moiety is not oxidized to the acid except for monosubstituted allenes [21]. In all other cases, the carbonyl oxygen participates as a nucleophile in the opening of the intermediate epoxide. From 2,2,5-trimethy]-3,4-hexadienal 67, for example, five different products can be synthesized selectively under different reaction conditions (Scheme 17.22). When p-toluenesulfonic acid (TsOH) is present or DMDO is formed in situ, then the initially formed allene (mono)oxide reacts with the aldehyde moiety to give 68 or 69. In the presence of excess DMDO and the absence of acid, three other products (70-72) can be formed via the spirodioxide intermediate. These reactions, however, seem to be less general compared with similar reactions of allenyl acids and allenyl alcohols. y-Allenylaldehydes 73 can be cyclized to five-membered hemiacetals 74 via the spirodioxide intermediate. 

Allenyl aldehydes undergo a ruthenium-catalyzed cycloaddition reaction with CO to afford reduced furopyridines in good yields (Equation 17) <2002AGE1584>. In a similar reaction, the furopyran derivative is formed. 

Following preliminary observations on allenyl alcohols from Gore27-31 and Balme32 along with Claesson and Olsnon,33 Marshall et al. demonstrated in a seminal publication34 that allenyl ketones (R3 = alkyl, Scheme 5.2) or allenyl aldehydes... 

Furthermore, Kang and coworkers [128,129] have developed a sequential silastannylation-allyl addition reaction upon reacting allenyl aldehydes... 

Kang et al. reported that the ruthenium-catalyzed intramolecular hetero-Pauson—Khand reaction of the allenyl aldehydes and ketones 387 gave the a-meth-ylene-y-butyrolactones 388 (Scheme 123).186... 

Intramolecular oxypalladation of the allenyl aldehyde 249 generates the intermediary alkenylpalladium complex 250, and subsequent carbonylation affords the unsaturated ester 251 in 88 % yield. Propylene oxide is added as a scavenger of HCl [107]. 

Silylstannation of the allenyl aldehyde 148 with 140 in THF at room temperature generated the allylstaimane 149, which attacked intramolecularly the formyl group to yield the cyclic homoallylic alcohol 150. Phosphine-free 7r-allylpalladium chloride was the most effective catalyst [48]. 

Recently, Wang reported a novel approach for the assembly of up-to-pentasub-stituted pyrroles 299 via an acidallenyl aldehydes 296 and anilines 297. It was further demonstrated that this transformation could also be efficiently catalyzed by Au(I)- and Ag salts. Surprisingly, a sulfanyl group in 298 underwent an intramolecular 1,2-migration via the proposed thitranium intermediate yielding the corresponding 2-thiopyrroles 299 (Scheme 8.106) [304]. 

Takimoto M, Kawamura M, Mori M, Sato Y (2011) Nickel-promoted carboxylation/cycli-zation cascade of allenyl aldehyde under an atmosphere of CO2. Synlett 2011 1423-1426... 

Pentacarbonyliron catalyzes the [4 -F 1]-cycloaddition of CO to allenyl ketones and allenyl aldehydes in high yields and with good stereoselectivity. This reaction was examined in 2-methyltetrahydrofuran (2-MeTHF) matrices where the substituted complex Fe(CO)4(2-MeTHF) was found to be produced upon photolysis of Fe(CO)s at 190-230 K. When Fe(CO)s was photolyzed at 230 K in 2-MeTHF in the presence of 5-methyl-3,4-hexadien-2-one and CO, the corresponding a-alkylidene butenolide was obtained (Scheme 4). The reaction proceeded via a dissociative process from Fe(CO)4(2-MeTHF). ... 

To meet the demand, the compound has been successfully synthesized by hydroamination/ cyclization of amino-allene 13" ° (Scheme 39.7). Enantio-selective addition of n-dibutyl zinc to allenyl aldehyde 10 using a chiral Ti catalyst (generated by heating the mixture of 11 and Ti(Ot-Pr)4 in dry toluene at 40-45 °C for 30 minutes) provides the corresponding hydroxyl... 

Amarasinghe, K.K.D. and Montgomery, J. (2002) Enantioselective total synthesis of (+)-testudinariol A using a new nickel-catalyzed allenyl aldehyde cydization./. Am. Chem. Soc., 124, 9366-9367. 

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