Aldehydes, reactions Alkenes

There are a few other methods for converting ketones or aldehydes to alkenes. When a ketone is treated with CH3CHBr2/Sm/Sml2, with a catalytic amount of CrCls, for example, the alkene is formed. In another reaction, an aldehydes reacted with EtCHBr(OAc) in the presence of Zn/CrCl3 to give the alkene. ... 

In a related reaction, alkenes can be added to aldehydes and ketones to give... 

Photocycloaddition Reactions of Carbonyl Compounds and Alkenes. Photocycloaddition of ketones and aldehydes with alkenes can result in formation of four-membered cyclic ethers (oxetanes), a process often referred to as the Paterno-Buchi reaction.196... 

A catalyst used for the u-regioselective hydroformylation of internal olefins has to combine a set of properties, which include high olefin isomerization activity, see reaction b in Scheme 1 outlined for 4-octene. Thus the olefin migratory insertion step into the rhodium hydride bond must be highly reversible, a feature which is undesired in the hydroformylation of 1-alkenes. Additionally, p-hydride elimination should be favoured over migratory insertion of carbon monoxide of the secondary alkyl rhodium, otherwise Ao-aldehydes are formed (reactions a, c). Then, the fast regioselective terminal hydroformylation of the 1-olefin present in a low equilibrium concentration only, will lead to enhanced formation of n-aldehyde (reaction d) as result of a dynamic kinetic control. 

The synthesis of aldehydes from alkenes known as hydroformylation using CO and hydrogen and a homogeneous catalyst is a very important industrial process [204]. Today, over seven million tons of oxoproducts are formed each year using this procedure, with the majority of butanal and butanol from propene. To further increase the efficiency of this process it can be combined with other transformations in a domino fashion. Eilbracht and coworkers [205] used a Mukaiyama aldol reaction as a second step, as shown for the substrate 6/2-63 which, after 3 days led to 6/2-65 in 91% yield via the primarily formed adduct 6/2-64 (Scheme 6/2.13). However, employing a reaction time of 20 h gave 6/2-64 as the main product. 

Vinylphosphonium bromide 208 reacts with Grignard reagents, forming alkylphospho-nium ylides. These ylides react with aldehydes, giving alkenes in a one-pot sequence. In this reaction, catalytic amounts of both copper and silver salts are necessary (equation... 

In a related reaction, alkenes can be added to aldehydes and ketones to give reduced alcohols 70. This has been accomplished by several methods,725 including treatment with... 

Exercise 16-35 A radical-chain reaction similar to that described for the air oxidation of benzaldehyde occurs in the peroxide-initiated addition of aldehydes to alkenes (see Table 10-3). Write a mechanism for the peroxide-induced addition of ethanal to propene to give 2-pentanone. 

This reaction is important for a number of reasons. It is an industrial synthesis of aldehydes from alkenes by the addition of carbon monoxide and hydrogen in the presence of a cobalt catalyst. A prime example is the synthesis... 

In a similar catalysed reaction alkenes are produced by the addition of monosilylated derivatives 168 to aldehydes in the presence of a catalytic amount of caesium fluoride in dimethyl sulphoxide (equation 138)210. 

The intramolecular coupling of an aldehyde and alkene at —78 °C, promoted by Sml2, in the presence of a ketone, has led to a tandem coupling-addition process. This reaction has proved to be synthetically very useful for the preparation of poly-oxygenated compounds (equation 139)523. This reductive coupling process may also be promoted in dry methanol,... 

Under very mild conditions, the Wittig-type reaction of dimesitylboron stabilized car-banions with arylketones and aldehydes yields alkenes in good yields (equation 142)530. The stereochemistry of the alkene produced may be controlled, depending upon conditions. 

The Prins Reaction is the acid-catalyzed of addition aldehydes to alkenes, and gives different products depending on the reaction conditions. It can be thought of conceptually as the addition of the elements of the gem-diol carbonyl hydrate of the aldehyde across the double bond. 

Reduction is an important reaction for the metabolism of compounds that contain reducible groups, such as aldehydes, ketones, alkenes, nitro groups,... 

Over the past ten years, absolute rate data have been reported on the kinetics of several bimolecular silene reactions in solution, including both head-to-tail and head-to-head dimerization the [l,2]-addition reactions of nucleophilic reagents such as water, aliphatic alcohols, alkoxysilanes, carboxylic acids and amines and the ene-addition, [2 + 2]-cycloaddition and/or [4 + 2]-cycloaddition of ketones, aldehydes, esters, alkenes, dienes and oxygen. The normal outcomes of these reactions are summarized in Scheme 1. 

Ene reaction. The ene reaction of aldehydes with alkenes catalyzed by (R)-1 and 4-A molecular sieves can provide homoallylic alcohols with marked enan-tioselectivity (equations I and II). 

These protocols can be regarded as promising because of their simplicity and broad scope. The conventional method for the production of aldehydes from alkenes consists of ozonolysis followed by workup under reducing conditions [72]. The ruthenium-based method, using either oxone or NaI04 as the oxidant, is an interesting alternative. The high selectivity to aldehyde versus carboxylic acid was reached by manipulation of the amount of terminal oxidant (2 Eq.) and the reaction time. 

A Pd-catalyzed oxidative cyclization of phenols with oxygen as stoichiometric oxidant in the noncoordinating solvent toluene has been developed for the synthesis of dihydrobenzo[ ]furans (Equation 136). Asymmetric variants of this Wacker-type cyclization have been reported by Hayashi and co-workers employing cationic palladium/2,2 -bis(oxazolin-2-yl)-l,l -binaphthyl (boxax) complexes <1998JOC5071>. Stoltz and co-workers have reported ee s of up to 90% when (—)-sparteine is used as a chiral base instead of pyridine <2003AGE2892, 2005JA17778>. Attempts to effect such a heteroatom cyclization with primary alcohols as substrates, on the other hand, led to product mixtures contaminated with aldehydes and alkene isomers, which is in contrast to the reactions with the Pd(ii)/02 system in DMSO <1995TL7749>. 

The enaminones are hydrogenated to y-amino alcohols with marked stereoselectivity. Ene reactions of aldehydes with -alkenes. Ethylaluminum dichloride in CHjCl,... 

They also applied this method to the intermolecular ene reactions of aliphatic and aromatic aldehydes with alkenes containing a disubstituted vinylic carbon, a potentially valuable route to homoallylic alcohols [50]. Proton-initiated rearrangements do not take place, because the alcohol-Lewis acid complex formed in the ene reaction reacts readily to give methane and a non-acidic aluminum alkoxide. Formaldehyde and excess Me2AlCl gave good yield of ene adducts with all types of alkene, as exemplified in Sch. 26. 

In a different type of reaction, alkenes are photooxygenated (with singlet O2, see 14-7) in the presence of a Ti, V, or Mo complex to give epoxy alcohols, such as 180, formally derived from allylic hydroxylation followed by epoxidation. " In other cases, modification of the procedure gives simple epoxidation. " Alkenes react with aldehydes and oxygen, with palladium-on-silica " or a ruthenium catalyst, " " ... 

Above 650 K, because of their weak C—H bonds, the reaction of aldehydes and alkenes with O2 can become important. 

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