Aldehydes with alkenes

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... 

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). 

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. 

It has long been known that unsymmetrical ketones can be prepared by the reaction of aldehydes with alkenes under free-radical reaction conditions. Recently the revision of this chemistry has been reported by the Roberts group [42], They introduced thiols as a polarity reversal catalyst for the addition of aldehydes to alkenes. Thiyl radicals are electrophilic, and therefore a polar Sh2 type transition state for the hydrogen transfer step from an aldehyde would be ideal in this situation. Indeed, the addition of aldehydes to a variety of alkenes can be effected by... 

The ene reaction of aldehydes with alkenes provides a potentially valuable route to homoallylic alcohols [cf. (14a) (14b)]. Coupling of isoprene with 3-methyl-... 

Lewis Acid Catalyzed Intermolecular Ene Reactions of Aldehydes with Alkenes. ... 

Lewis acid catalyzed ene reactions have been shown to have a broad scope which complements thermal ene reactions. In many cases complex products can be produced with excellent control of stereo- and regiochemistry. During our exploration of these reactions we have found related Lewis acid catalyzed additions of o,p-unsaturated ketones and aldehydes and aldehydes with alkenes which give rise to open zwitterions which imdergo controlled reactions to give cyclobutanes, Y-chloroalcohols, and new carbonyl compounds. From the above results it is clear that or-ganoaluminum compounds, due to their ability to act as proton scavengers and alkyl donors, have an important role to play in the development of Lewis acid catalyzed reactions. 

Other Unsaturated Alcohols. Dimethylaluminium chloride has been found to be a useful catalyst for the ene reaction of aliphatic and aromatic aldehydes with alkenes (Scheme 16) to produce homoallylic alcohols/ by acting as a mild Lewis acid and proton scavenger rapid decomposition of the product alcohol-Lewis acid complex (42), a strong proton acid species, gives methane and a non-acidic alkoxide, thus avoiding protonation of the carbon-carbon double bond in the alkene or ene adduct, 1,1-Disubstituted alkenes are the most reactive under these conditions, and the yields of ene additions to formaldehyde are also improved. 

Homoallylic Alcohols. Full details have appeared of the ene reactions of aldehydes with alkenes, catalysed by dimethylaluminium chloride (Scheme 8) (6, 166). ... 

Methylarsine, trifluoromethylarsine, and bis(trifluoromethyl)arsine [371-74-4] C2HAsF, are gases at room temperature all other primary and secondary arsines are liquids or solids. These compounds are extremely sensitive to oxygen, and ia some cases are spontaneously inflammable ia air (45). They readily undergo addition reactions with alkenes (51), alkynes (52), aldehydes (qv) (53), ketones (qv) (54), isocyanates (55), and a2o compounds (56). They also react with diborane (43) and a variety of other Lewis acids. Alkyl haUdes react with primary and secondary arsiaes to yield quaternary arsenic compounds (57). 

In 1959 Carboni and Lindsay first reported the cycloaddition reaction between 1,2,4,5-tetrazines and alkynes or alkenes (59JA4342) and this reaction type has become a useful synthetic approach to pyridazines. In general, the reaction proceeds between 1,2,4,5-tetrazines with strongly electrophilic substituents at positions 3 and 6 (alkoxycarbonyl, carboxamido, trifluoromethyl, aryl, heteroaryl, etc.) and a variety of alkenes and alkynes, enol ethers, ketene acetals, enol esters, enamines (78HC(33)1073) or even with aldehydes and ketones (79JOC629). With alkenes 1,4-dihydropyridazines (172) are first formed, which in most cases are not isolated but are oxidized further to pyridazines (173). These are obtained directly from alkynes which are, however, less reactive in these cycloaddition reactions. In general, the overall reaction which is presented in Scheme 96 is strongly... 

Aldehydes react with a-nitroacetophenone in refluxing toluene to generate a 3-acetyl-2-isoxazoline (78USP4092327), while a-nitroacetophenone oxides react with alkenes to provide 2-isoxazolines (Scheme 121) (79ZOR735, 79ZOR2408, 80CPB479>. 

Osmium tetroxide, reaction with alkenes, 235-236 toxicity of, 235 Oxalic add, structure of, 753 Oxaloacetic acid, structure of, 753 Oxetane, reaction with Grignard reagents, 680 Oxidation, 233, 348 alcohols, 623-626 aldehydes, 700-701 aldoses, 992-994 alkenes, 233-236 biological, 625-626 phenols, 631 sulfides, 670 thiols, 668... 

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. 

Lanthanide triflates catalyze the Diels-Alder reaction of imines, generated from anilines and aldehydes, with both dienes and alkenes [26]. Thus N-benzyl-ideneaniline in the presence of Yb(OTf)3 (Scheme 6.16) reacts in organic solvent with open-chain dienes, such as Danishefsky s diene, to give tetrahy-dropyridine derivatives, while with cyclopentadiene and vinylethers and vinylthioethers it works like azadiene in both organic solvent and aqueous medium, affording tetrahydroquinoline derivatives. 

Another interesting biooxygenation reaction with alkenes, recently identified, represents an enzymatic equivalent to an ozonolysis. While only studied on nonchiral molecules, so far, this cleavage of an alkene into two aldehydes under scores the diversity of functional group interconversions possible by enzymatic processes [121,122]. 

In the presence of metal catalysts such as rhodium compounds, aldehydes can add directly to alkenes to form ketones. The reaction of co-alkenyl aldehydes with rhodium catalyst leads to cyclic ketones, with high enantioselectivity if chiral ligands are employed. Aldehydes also add to vinyl esters in the presence of hyponitrites and thioglycolates. ° ... 

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. ... 

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