Aldehydes 1.3- dienes

This methodology has been expanded to synthesize allyl silanes from silylated l,3-dienes. Both Z- and -isomers could be obtained by varying the ligand used in the reaction. It should be noted that an increase in yield was observed when PPhs was added to the nickel-NHC system. While no erosion in selectivity was observed, the phosphine is proposed to stabilize the active nickel species [95]. Finally, use of a chiral NHC allowed for an enantioselective coupling of a variety of aldehydes, 1,3-dienes, and silanes [96]. 

Danishefsky, S. J. Simoneau, B. Total synthesis of ML-236A and compactin by combining the lactonic (silyl) enolate rearrangement and aldehyde-diene cyclocondensation technologies./. Am. Chem. Soc. 1989, 111, 2599-2604. 

This method was used in the stereoselective synthesis of cis- and /ran -hemicaronic aldehydes 9 which were prepared in high enantiomeric purity starting from optically active sorbic aldehyde diene tricarbonyliron complex 6 via Wittig olefination, diazo ester cyclopropanation (copper powder), and further conversion with release of the cyclopropane from the complex and ozonolysis. ... 

Promising results have been reported by Corey using cationic oxazaborinane complex 16 as an aldehyde-diene cycloaddition catalyst (Scheme 20) [70]. a-Substituted aldehydes and four dienes are reported to undergo low-temperature (-94 °C) Diels-Alder reaction to give adducts in high exo selectivity and excellent enantioselection. The catalyst is prepared in seven steps and hgand recovery after the reaction is 85% catalyst decomposition occurs above -60 °C. 

Aldehyde Diene Conditions d.r.d (synjanti) Product Yield (%)... 

Some exceptions to the general rules occur. Cyclopentene is completely combusted, undoubtedly because of the high reactivity of cyclo-pentadiene. 4,4-Dimethyl-1-pentene is expected to produce an unsaturated aldehyde, but instead 2,3-dimethylpentadiene is the initial product. A methyl shift from a quarternary carbon is apparently easy, permitting formation of a diene instead of the oxygenated compound. 3,3-Dimethyl-l-butene is not expected to react at all under the general rules, but here also a methyl shift occurs so that diene, olefin aldehyde, diene aldehyde, and diene dialdehyde are formed. The reactivity of the latter olefin relative to 1-butene, measured by oxidation of a mixture at low conversion, was 0.21, while that of 4,4-dimethyl-1-pentene was 0.75. These reactivities suggest that isomerization occurs before reaction for 3,3-dimethyl-l-butene, while isomerization probably occurs after the aUyl intermediate is formed in the case of the pentene. 

Several fundamentally different mechanisms have been proposed for aldehyde-diene reductive couplings, including those involving metallacyclic intermediates as well as distinct mechanisms involving reaction initiation by Ni(0)... 

Keywords Indoles, aldehydes, dienes, Ga(III) salts, dichloromethane, room temperature, one-pot three-component [4+3]-cycloaddition, cyclohepta[ft]indoles... 

The 5-oxohexanal 27 is prepared by the following three-step procedure (1) 1,2-addition of allylmagnesium bromide to an a, / -unsaturated aldehyde to give the 3-hydroxy-1,5-diene 25, (2) oxy-Cope rearrangement of 25 to give 26, and (3) palladium catalyzed oxidation to afford 27. The method was applied to the synthesis of A -2-octalone (28), which is difficult to prepare by the Robinson annulation[25]. 

The reduction of acyl halides with hydrogen to form aldehydes using Pd catalyst is well known as the Rosenmund reduction[756]. Some acyl chlorides give decarbonyiation products rather than aldehydes under Rosenmund conditions. The diene 890 was obtained by decarbonyiation in an attempted Rosenmund reduction of acetyloleanolic acid chloride (889)[757], Rosenmund reduction of sterically hindered acyl chlorides such as diphenyl- and tnpheny-lacetyl chloride (891) gives the decarbonylated products 892[758],... 

Pd-cataly2ed reactions of butadiene are different from those catalyzed by other transition metal complexes. Unlike Ni(0) catalysts, neither the well known cyclodimerization nor cyclotrimerization to form COD or CDT[1,2] takes place with Pd(0) catalysts. Pd(0) complexes catalyze two important reactions of conjugated dienes[3,4]. The first type is linear dimerization. The most characteristic and useful reaction of butadiene catalyzed by Pd(0) is dimerization with incorporation of nucleophiles. The bis-rr-allylpalladium complex 3 is believed to be an intermediate of 1,3,7-octatriene (7j and telomers 5 and 6[5,6]. The complex 3 is the resonance form of 2,5-divinylpalladacyclopentane (1) and pallada-3,7-cyclononadiene (2) formed by the oxidative cyclization of butadiene. The second reaction characteristic of Pd is the co-cyclization of butadiene with C = 0 bonds of aldehydes[7-9] and CO jlO] and C = N bonds of Schiff bases[ll] and isocyanate[12] to form the six-membered heterocyclic compounds 9 with two vinyl groups. The cyclization is explained by the insertion of these unsaturated bonds into the complex 1 to generate 8 and its reductive elimination to give 9. 

Addition of HCN to unsaturated compounds is often the easiest and most economical method of making organonitnles. An early synthesis of acrylonitrile involved the addition of HCN to acetylene. The addition of HCN to aldehydes and ketones is readily accompHshed with simple base catalysis, as is the addition of HCN to activated olefins (Michael addition). However, the addition of HCN to unactivated olefins and the regioselective addition to dienes is best accompHshed with a transition-metal catalyst, as illustrated by DuPont s adiponitrile process (6—9). 

Cyclopropanes can also be obtained by the reaction of vinyltrialkylborates with aldehydes followed by treatment with phosphoms pentachloride and base (300), and by the rearrangement of 5-substituted alkynyltrialkylborates (308). It is also possible to utilize this approach for the synthesis of five- and six-membered rings (3). Trans-1,4-elimination ia cycHc systems leads to the formation of stereodefined acycHc 1,5-dienes or medium-ring dienes, depending on the starting compound (309). 

Miscellaneous Curing Reactions. Other functional groups can react with the thiol terminal groups of the polysulfides to cross-link the polymer chains and build molecular weight. For example, aldehydes can form thioacetals and water. Organic and inorganic acids or esters can form thioesters. Active dienes such as diacrylates can add to the thiols (3). Examples of these have been mentioned in the Hterature, but none have achieved... 

The reversible addition of sodium bisulfite to carbonyl groups is used ia the purification of aldehydes. Sodium bisulfite also is employed ia polymer and synthetic fiber manufacture ia several ways. In free-radical polymerization of vinyl and diene monomers, sodium bisulfite or metabisulfite is frequentiy used as the reduciag component of a so-called redox initiator (see Initiators). Sodium bisulfite is also used as a color preventative and is added as such during the coagulation of crepe mbber. 

Zirconium hydrides undergo 1,2-addition with 1,3-dienes to give y,5-unsaturated complexes in 80—90% yield. Treatment of these complexes with CO at 20°C and 345 kPa (50 psi) followed by hydrolysis gives y,5-unsaturated aldehydes (235). 

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