Allenic aldehyde

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. 

Trimethylsilylation with trimethylchlorosilane affords the corresponding allene derivative, hydroxyalkylation with aldehydes and ketones gives mixtures of comparable amounts of acetylenic and allenic carbinols. 

Ojj 1.5204, in 52% yield. There was a viscous residue of about 1 g, probably resulting from polymerization of the allenic aldehyde (note 2). Redistillation gave about the same amount of residue. 

Note 1. At higher temperatures the adduct decomposes and yields of the allenic aldehyde are lower. 

Note 2. A similar experiment v/ith C H9-CH=C=CH2 gave only traces of the allenic aldehyde and much resinous residue. 

Aryl or alkenyl halides attack the central carbon of the allene system in the 2,3-butadien-l-ol 120 to form the 7r-allyl intermediate 121, which undergoes elimination reaction to afford the o,/3-unsaturated ketone 122 or aldehyde. The reaction proceeds smoothly in DMSO using dppe as a ligandflOl]. 

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

Abstract The photoinduced reactions of metal carbene complexes, particularly Group 6 Fischer carbenes, are comprehensively presented in this chapter with a complete listing of published examples. A majority of these processes involve CO insertion to produce species that have ketene-like reactivity. Cyclo addition reactions presented include reaction with imines to form /1-lactams, with alkenes to form cyclobutanones, with aldehydes to form /1-lactones, and with azoarenes to form diazetidinones. Photoinduced benzannulation processes are included. Reactions involving nucleophilic attack to form esters, amino acids, peptides, allenes, acylated arenes, and aza-Cope rearrangement products are detailed. A number of photoinduced reactions of carbenes do not involve CO insertion. These include reactions with sulfur ylides and sulfilimines, cyclopropanation, 1,3-dipolar cycloadditions, and acyl migrations. 

The product in this case is an allene, ° but such shifts can also give triple-bond compounds or, if Y=OH, an enol will be obtained that tautomerizes to an a,P-unsaturated aldehyde or ketone. 

Enamines can also be converted to amino alcohols via hydroboration. Allene-boranes react with aldehydes to give alkyne-alcohols. ... 

AUylzirconium complexes are conveniently obtained by the regio- and stereoselective hydrozirconation of allene [127-133] and can be, for example, used subsequently for the MAO-catalyzed allylzirconation of alkynes to prepare enyne derivatives [132]. Alternatively, the preparation of (E)-l,3-dienes from aldehydes and the appropriate allylstannane zirconocene derivative (R = SnBu,) is accomplished (Scheme 8-17) [131], Note that addition of [Cp2Zr(H)Cl[n (1) on the aUenyl reagent with the... 

In order to synthesise the pyrrolidine alkaloid, (-l-)-197B, bis-(i ,i )-tri-fluoromethanesulfonamide ligand was employed in the enantioselective addition of Zn( -Bu)2 to an allene-aldehyde, alfording the corresponding (i )-alcohol in 70% yield and 94% ee (Scheme 3.52). ... 

The allenic stannanes react with aldehydes under the influence of Lewis acids such as BF3 and MgBr2. Unbranched aldehydes are not very stereoselective, but branched aldehydes show a strong preference for the syn adduct. 

The allenic stannanes can be transmetallated by treatment with SnCl4, a reaction that results in the formation of the a propargyl stannane. If the transmetallation reaction is allowed to equilibrate at 0°C, an allenic structure is formed. These reagents add stereospecifically to the aldehyde through cyclic TSs.194... 

Oda et al. reported that under reflux conditions, the zinc-promoted reaction of 2,3-dichloro-l-propene with aldehydes and ketones in a two-phase system of water and toluene containing a small amount of acetic acid gave 2-chloroallylation products (Eq. 8.31).64 No conversion occurred when tin was used as the promoter. The absence of water completely shuts down the reaction. Interestingly, the action of 2,3-dichloropropene plus zinc powder in aqueous ethanol gives the dechlorination product, allene.65... 

The mechanism of [3 + 2] reductive cycloadditions clearly is more complex than other aldehyde/alkyne couplings since additional bonds are formed in the process. The catalytic reductive [3 + 2] cycloaddition process likely proceeds via the intermediacy of metallacycle 29, followed by enolate protonation to afford vinyl nickel species 30, alkenyl addition to the aldehyde to afford nickel alkoxide 31, and reduction of the Ni(II) alkoxide 31 back to the catalytically active Ni(0) species by Et3B (Scheme 23). In an intramolecular case, metallacycle 29 was isolated, fully characterized, and illustrated to undergo [3 + 2] reductive cycloaddition upon exposure to methanol [45]. Related pathways have recently been described involving cobalt-catalyzed reductive cyclo additions of enones and allenes [46], suggesting that this novel mechanism may be general for a variety of metals and substrate combinations. 

Aldehydes and ketones also add to allenes to form oxetanes.ai0,111) Further reaction of the oxetanes produced with excited carbonyls results in dioxaspiro[3.3]heptane derivatives(111) ... 

Lauryl alcohol has been prepared by the reduction of the aldehyde with zinc dust and acetic acid 1 by the reduction of esters of lauric acid with sodium and absolute alcohol 2 or with sodium, liquid ammonia, and absolute alcohol 3 by the reduction of lauramide with sodium and amyl alcohol.4 The method in the above procedure is essentially that described by Levene and Allen.5... 

Clavepictines A and B (210 and 211, respectively) were obtained from the allenic ester 227. The reduction of its ester group to aldehyde, followed of addition to the latter of hexylmagnesium bromide, OH protection, and N-deprotection gave compound 228. A silver(i)-mediated cyclization of this compound afforded quinolizidine 229 and its C-6 epimer in a 7 1 ratio (Scheme 44). The former compound was readily converted into the target alkaloids <1997JOC4550>. 

Allen (106) also studied cobalt hydroformylation with a polymer-bound catalyst. The polymer was formed from diphenyl-p-styrylphosphine cross-linked with divinylbenzene. 2-Hexene was the substrate, and reaction conditions were 175°C and 1500-3000 psi of 1/1 H2/CO. The product aldehyde was 55% linear, and the effluent product solution contained 20-50 ppm cobalt. 

A study of the reactions of butadiene, isoprene, or allene coordinated to nickel in a metallacycle, with carbonylic compounds, has been reported by Baker (example 11, Table IV). In the presence of phosphines, these metallacycles adopt a cr-allyl structure on one end and a ir-allyl structure on the other, as mentioned in Section II,A,1. The former is mainly attacked by aldehydes or electrophilic reagents in general, the latter by nucleophiles (C—H acids, see Table I, or amines, see Table IX). 

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