Aldehydes alkynyl

Table 1.6 Asymmetric Diels-Alder reactions of alkynyl aldehydes catalyzed by 8 [lOc]...

Optically active alkynyl alcohols can, however, be conveniently prepared by the addition of dialkylzinc reagents of alkynyl aldehydes catalyzed by the chiral ligand (S)-l-methyl-a,a-diphenyl-2-pyrrolidine methanol33-34. 

In the hydroboration of terminal alkenes, carrying a ketone or aldehyde group, with a variety of borane reagents, dicyclohexylborane has been identified as the most efficient reagent. Analogous hydroboration of alkynyl ketones and alkynyl aldehydes with dicyclohexylborane yields the corresponding olefinic carbonyl compounds after protonation, or dicarbonyl compounds after oxidation. ... 

In 2006, Zeitler demonstrated the use of alkynyl aldehydes in redox esterification [114]. As in previous examples, the author proposes the formation of an activated carboxylate that acts as an acylating agent Eq. 19. A variety of a,P-unsaturated carboxylic esters 199 are formed in moderate yields with E-selectivity up to >95 5. 

Alcaide et al. (68,69) recently published their smdies of the intramolecular 1,3-dipolar cycloaddition reactions of alkynyl-p-lactams in which they found that the desired cycloaddition was in competition with a reverse-Cope elimination. The reaction of alkynyl aldehydes 37a-c with Al-methylhydroxylamine afforded a mixture of products depending on the reaction conditions and the chain length separating the alkyne and the lactam (Scheme 1.8). Thus, up to three separate... 

Isotellurazoles 4 were obtained in low yields (3-11%) by the one-pot reaction of alkynyl ketones with hydroxylamino-O-sulfonic acid and K2Te in aqueous solution containing sodium acetate (83S824 87H1587). A plausible mechanism of the reaction includes formation of the oxime derivative and subsequent nucleophilic addition of telluride anion to the triple bond followed by cyclization to 4. The reaction is accompanied by the formation of telluro bis(alkenyl ketones) 5 in yields approximately equal to those of 4. When alkynyl aldehydes are used instead of ketones, the single reaction products are the tellurobis(alkenyl nitriles) 6 (83S824). 

Alkynyl alcohols, silylative lactonization, 11, 493 Alkynyl aldehydes, in [5+2+l]-cycloadditions, 10, 632 Alkynyl alkali metal derivatives, characteristics, 2, 17 Alkynyl amides, in [5+2+l]-cycloadditions, 10, 632... 

Diastereoselective aldol coupling of alkynyl aldehydes.3 The Co2(CO)6 complexes (2) of alkynyl aldehydes react with silyl enol ethers to form aldols with... 

The intramolecular nitrone-alkene cycloaddition reaction of monocyclic 2-azetidinone-tethered alkenyl(alkynyl) aldehydes 211, 214, and 216 with Ar-aIkylhydroxylamincs has been developed as an efficient route to prepare carbacepham derivatives 212, 215, and 217, respectively (Scheme 40). Bridged cycloadducts 212 were further transformed into l-amino-3-hydroxy carbacephams 213 by treatment with Zn in aqueous acetic acid at 75 °C. The aziridine carbaldehyde 217 may arise from thermal sigmatropic rearrangement. However, formation of compound 215 should be explained as the result of a formal reverse-Cope elimination reaction of the intermediate ct-hydroxy-hydroxylamine C1999TL5391, 2000TL1647, 2005EJ01680>. 

More recently, the scope of the Ni catalysed alkyne carbozincation has been extended to the cases of co-alkynyl aldehydes and even mixtures of aldehydes and alkynes.65 These reactions are generally accompanied by alkylation with organozincs (Scheme 11.20). 

The formation of bicyclic nitrones of the 2-azetidinone A-oxide type, 32 and (33), has been achieved in a two-step route, through condensation of the corresponding 2-azetidinone tethered-alkenyl(alkynyl)aldehyde with hydroxylamine followed by phenylselenyl bromide treatment <02JOC7004>. 

The stereochemical course of several Co2(CO)6-mediated reactions has been studied. For example, although alkynyl aldehydes undergo crossed aldol condensation with trimethylsilyl enol ethers with little stereoselectivity, their hexacarbonyldicobalt derivatives react with moderate to excellent syn diastereoselectivity.96 101 The mechanism behind this selectivity has not been fully elucidated and is complicated by the lluxional nature of the intermediate cations. This stereoselective reaction has been successfully applied to the synthesis of /3-lactam antibiotics.100... 

In the studies on the synthesis of the antitumor agents esperamicin and calicheamicin by Magnus et al. [93], an aldol reaction was found suitable for macrocyclization after a number of unsuccessful attempts. Thus, as shown in Scheme 54, the diynene core structure (165) of the two antitumor agents was synthesized from the dicobalt hexacarbonyl derivative 163. When 163 was treated with n-BujBOTf/DABCO/EtjN in CHzClj-THF the aldol product 164 was isolated as a single stereoisomer in 45% yield. Although alkynyl aldehydes undergo similar crossed aldol condensation, their dicobalt hexacarbonyl derivatives react with moderate to excellent syn diastereoselectivity [94]. 

Optically active aliphatic propargylic alcohols are converted to corticoids (90% ee) via biomimetic polyene cyclization, and to 5-octyl-2(5ii)-furanone. The ee s of propargylic alcohols obtained by this method are comparable with those of the enantioselective reduction of alkynyl ketones with metal hydrides, catalytic enantioselective alkylation of alkynyl aldehydes with dialkyIzincs using a chiral catalyst ((S)-Diphenyl(l-methylpyrrolidin-2-yl)methanol) (DPMPM), and the enantioselective alkynylation of aldehydes with alkynylzinc reagents using A(A-dialkylnorephedrines. °... 

Under the same conditions even free alkynyl aldehydes undergo a 1,4-addition to propargylic acid esters (eq. (6)) [14]. 

The most dramatic of all these reactions is the Eschenmoser fragmentation30 - a general route to alkynyl aldehydes 189 and ketones. The tosylhydrazone 186 of an epoxyketone 185 gives an anion on treatment with base that fragments once 187 to give an alkene and again 188 in the reverse direction 188 to give the alkyne. 

Variations on this theme include the use, as synthons for the 1,3-dicarbonyl component, of P-chloro-a,P-unsaturated ketones, or of conjugated alkynyl aldehydes. ... 

Heterocyclization of alkynyl aldehydes and imines proceeds through two different mechanistic pathways (Scheme 95, routes a and b). A Lewis acidic transition metal is coordinated by a heteroatom of C=Y, the nucleophilic addition of Nu- to the electron-deficient... 

The enantioselective addition of dialkylzinc reagents to alkynyl aldehydes catalysed by ( )-(+)-(l-methylpyrrolidin-2-yl)diphenylmethanol has been described. Thus the laevorotatory alcohol 102 was obtained in 78% enantiomeric excess (equation 15). The action of diethylaluminium chloride on alkynyllithium compounds yields ether-free diethylalkynylalanes 103, which undergo conjugate addition to nitroalkenes (equation 16). Conjugate addition also occurs in the reactions of (l-alkynyl)diisopropoxyboranes 104 (R = Bu, t-Bu or Ph) with a,j5-unsaturated ketones 105 (R = H, Me or Ph R = Me, hexyl or Ph) (equation 17). ... 

A route in which a synthon for such a dialdehyde is central depends on ortho lithiation of an aryl bromide for conversion to ortho bromoaryl aldehyde, then palladium-catalysed replacement of the halide with an alkyne, subsequent reaction with ammonia producing the isoquinoline. The sequence below shows how this type of approach can be used to produce naphthyridine mono-A-oxides by reaction of the alkynyl-aldehyde with hydroxylamine instead of ammonia. 

J In principle the double bond may be constructed in two ways using the Wittig reaction. The solution strtSwn is the more likely. The alternative would require an alkynyl aldehyde, a compound that is difficult to prepare and is not very stable. 

Scheme 7.22 Stereoselective prolinol Ik catalysed cross-aldol reactions employing alkynyl aldehydes and formaldehyde.

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