Aldehydes vinylidenation

It has been shown52 that under similar conditions reduction of the nitrile groups in cellulose ethyl cyanate and of those in the copolymer of vinylidene cyanide with vinyl acetate, proceed simultaneously in two directions with the formation of aldehyde and amine groups. g+ g ... 

In 1998, Wakatsuki et al. reported the first anti-Markonikov hydration of 1-alkynes to aldehydes by an Ru(II)/phosphine catalyst. Heating 1-alkynes in the presence of a catalytic amount of [RuCljlCgHs) (phosphine)] phosphine = PPh2(QF5) or P(3-C6H4S03Na)3 in 2-propanol at 60-100°C leads to predominantly anti-Markovnikov addition of water and yields aldehydes with only a small amount of methyl ketones (Eq. 6.47) [95]. They proposed the attack of water on an intermediate ruthenium vinylidene complex. The C-C bond cleavage or decarbonylation is expected to occur as a side reaction together with the main reaction leading to aldehyde formation. Indeed, olefins with one carbon atom less were always detected in the reaction mixtures (Scheme 6-21). 

The alternative building scheme C2 + Q was used by Petasis and Hu [89], who reacted various aldehydes and ketones with alkenyltitanocene derivatives 172 to obtain the corresponding allenes 173 in high chemical yields (Scheme 2.54). The reaction probably proceeds via titanocene vinylidene complexes, which can also be trapped with alkynes and isocyanides to afford allenylketene imines [90],... 

SCHEME 13. Conversion of aldehydes into alkynes under homologation. Application of hydride shifts in vinylidene carbenoids... 

This treatment can be extended without mrxlification to polymers obtained from vinylidene monomers with different substituents (CH2=CR R2) and from aldehydes (RCHO) in which the oxygen atom replaces the methylene group. 

Reactions with dioxygen generally afford the corresponding metal carbonyl derivatives, with loss of organic aldehyde or acid. This reaction can be expressed as an analog of multiple bond metathesis and corresponds to oxidation of vinylidene to CO [46]. Oxidation of OsHCl(=C=CHPh)(L)2 affords the styryl complex 0sC102( -CH=CHPh)(L)2 [243]. 

The hydrative cyclization involves the formation of a ruthenium vinylidene, an anti-Markovnikov addition of vater, and cyclization ofan acylmetal species onto the alkene. Although the cyclization may occur through a hydroacylation [32] (path A) or Michael addition [33] (path B), the requirement for an electron- vithdra ving substituent on the alkene and lack of aldehyde formation indicate the latter path vay to be the more likely mechanism. Notably, acylruthenium complex under vent no decarbonylation in this instance. 

Whereas the Markovnikov addition of carboxylic acids to propargylic alcohols produces P-ketoesters, resulting from intramolecular transesterification [30, 31], the addition to propargylic alcohols in the presence of Ru(methallyl)2(dppe) 1 at 65 °C leads to hydroxylated alk-l-en-l-yl esters via formation of a hydroxy vinylidene intermediate [32, 33]. The stereoselectivities are lo ver than those obtained from non-hydroxylated substrates. These esters, which are protected forms of aldehydes, can easily be cleaved under thermal or acidic conditions to give conjugated enals, corresponding to the formal isomerization products of the starting alcohols (Scheme 10.6). 

The prevailing chirality of the aldehyde produced using ( — )-DIOP as the asymmetric ligand is [ (R) ] for vinyl olefins where the asymmetric carbon atom arises from the attack of carbon monoxide at the carbon atom in position 2. The same chirality [ (R) ] is found also for vinylidene olefins where the asymmetric carbon atom arises from the attack of a hydrogen atom on the same carbon atom. 

One of the most interesting reactions of cationic vinylidene complexes is that with dioxygen, which affords the carbonyl cation and the corresponding aldehyde (41) ... 

Terminal alkynals (113) of appropriate length (n = 1, 2) and substitution [X = C(C02-Me)2, C(CH2OR)2, NTs, and others] have been cyclized with decarbonylation to cycloalkenes (114), using a ruthenium(I) catalyst.348 In some cases, cycloisomerization to give conjugated aldehyde occurred. Both processes are believed to involve catalytic ruthenium vinylidenes. 

Small chiral organic molecules may catalyze the asymmetric addition of ketones, and aldehydes to electron-deficient olefins, such as vinylidene acetones, nitroole-fins, enones, and vinyl sulfones. In this chapter we will describe the inter- and intramolecular reactions in which activation of the carbonyl compound takes place via enamine formation. 

The mechanism of this reaction was investigated in detail by Wakatsuki [13] by isolation of intermediates, deuterium-labeling experiments and theoretical calculations. The postulated catalytic cycle involves first the protonation of a Ru(II)-alkyne species to give a Ru(IV)-vinylidene intermediate via a Ru(IV)-vinyl species. The nucleophilic addition of water to the a-carbon of the vinylidene ligand followed by reductive elimination affords the aldehyde (Scheme 8.3). 

The diacetyl-substituted 2-vinylidene 1,3-dithiolane 645 was a much more effective transdithioacetalization reagent than 643 and gave the 1,3-dithiolanes 644 in 70-99% yields (Equation 88). Moreover, 645 was not only a nonthiolic, odorless 1,2-dithiol equivalent but also exhibited high chemoselectivity for protection of aldehyde in the presence of ketone <2004SL999>. 

H3C)2C=CH-0-CH2-C=C-C00C2H5 145 6 COOC2H5 H C=C=<. CHO X HsC u 3,3-Dimethyl-2-vinyliden-hernstein-4-aldehyd-1 -sdure-ethylester 69 49b 59... 

It seems unlikely then that carbonyl (ketone and aldehyde) formed by thermal breakdown of hydroperoxides are important sensitisers for photo-oxidation of LDPE in normally processed polymers. The evidence is consistent with the theory that all.ylic hydroperoxide derived from vinylidene is the important photo-initiator initially present under these conditions. Vinylidene disappears as a concomitant of hydroperoxide photolysis, initiating photo-oxidation in a manner analogous to its function in thermal oxidation. 

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