Vinylidene complexes imines

A chromium(O) pentacarbonyl-methylene chloride complex 131 was formed under irradiation, which reacted with an alkyne to form a vinylidene complex 132. Complex 132 further reacted with an imine or a dialkylcarbodimide to afford /3-lactams after decomplexation of chromium (Scheme 58).233... 

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],... 

Terminal alkynes readily react with coordinatively unsaturated transition metal complexes to yield vinylidene complexes. If the vinylidene complex is sufficiently electrophilic, nucleophiles such as amides, alcohols or water can add to the a-carbon atom to yield heteroatom-substituted carbene complexes (Figure 2.10) [129 -135]. If the nucleophile is bound to the alkyne, intramolecular addition to the intermediate vinylidene will lead to the formation of heterocyclic carbene complexes [136-141]. Vinylidene complexes can further undergo [2 -i- 2] cycloadditions with imines, forming azetidin-2-ylidene complexes [142,143]. Cycloaddition to azines leads to the formation of pyrazolidin-3-ylidene complexes [143] (Table 2.7). 

The generation of four-membered ring systems can be accomplished by a cycloaddition process under photochemical conditions or with special substrates under thermal conditions. Iron-vinylidene complexes belong to such a class of special substrates where a thermal [2 + 2]-cycloaddition is possible. If imines are used, a hetero-[2 + 2]-cycloaddition with an iron-vinylidene complex leads to an iron-carbene complex attached to an azetidine ring system, as reported by Barrett and coworkers (Scheme 9.20) [46, 47]. The oxidation of these iron-carbene complexes leads to [3-lactams 27. Interestingly, the application of 2-thiazolines generates penam... 

The chemistry of iron vinylidene complexes is dominated by the electrophilicity of the carbon atom adjacent to the iron organometallic unit. While addition of water leads to an acyl complex (i.e., the reverse of the dehydration shown in equation 10), addition of an alcohol leads to a vinyl ether complex. Similarly, other iron vinyl complexes can be prepared by the addition of thiolate, hydride, or an organocuprate (Scheme 33). " The nucleophilic addition of imines gave enaminoiron intermediates that could be further elaborated into cyclic aminocarbenes. This methodology has been used to provide access to /3-lactams and ultimately penicillin analogs, and good diastereoselectivities were observed (6 1-15 1) (Scheme 34). 04 Iso, vinylidene complexes are intermediates in cyclizations of alkynyl irons with substituted ketenes, acid chlorides, and related electrophiles an example is shown (equation 11). These cyclizations led to the formation of a series of isolable and characterizable cyclic vinyl iron complexes. 

The incorporation of the second equivalent of imine can be prevented in these reactions if a vinylidene complex, such as (31), is employed which is 3optimized conditions indicated, the reaction of (31) with A -meAyl benzaldehyde imine will provide the cycloadduct (32) in quite good yield. A rather unc odox oxidation procedure (BU4NNO2, 6.5 kbar 1 bar = 10 Pa) is required for the effective cleavage of the cationic complex (32) to the 3-lactam (33). This reaction was shown to involve a two-step process, since the salt (37) could be isolated in 80% yield by column chromatography if the reaction was stO[q)ed shortly after the reaction mixture was Ivought to room tenq>erature. The reaction with the cyclic thioimidate (34) indicates that vinylidene complexes can be useful in the synthesis of functionalized 3-lactams in good yields with high stereoselectivity. 

In some cases, vinylidene complexes undergo [2-t-2] reactions that are characteristic of Fischer and Schrock carbene complexes. However, these [2+2] reactions involving vinylidene complexes can result from nucleophilic addition at the central carbon, rather than a concerted [2+2] process. For example, the reaction of an imine with the iron-vinylidene complex in Equation 13.28 leads to formation the product of a [2+2] reaction between the carbon-nitrogen double bond and the carbon-carbon double bond. ° - This reaction is believed to occur by nucleophilic attack of the nitrogen at the central carbon, followed by ring closure at the p-carbon, instead of a concerted [2+2] process. 

The equilibrating mixture of ethylidyne complex 22 and vinylidene complex 23 have been found to give a variety of new reactions with imines, azines, and carbodiimides (see Scheme VUI) [5]. Although the products of the reactions described below are... 

Also, bi- and trimetallic cumulene complexes, such as M=C=M, M=M=C, M=M=M and M=C=C=M are known. Cationic ruthenium allenylidene complexes are used as catalysts for ring closing metathesis reactions. Nonlinear optical properties have been measured for the Group 6 cumulenylidene complexes. Also, cationic chromium or iron vinylidene complexes undergo [2-1-2] cycloaddition reactions across imines to give fi-lactams. This reaction is useful for the synthesis of j8-lactam antibiotics. ... 

Vinylidene complexes of manganese and rhenium, generated in situ, undergo [2+2] cycloaddition reactions with imines to form 52. ... 

The vinylidene complexes (CO)5W=C=CPh2 react with imines and triphenylketen-imines to give [2+2] cycloadducts AUenylidene complexes of chromium 56 also undergo [2+2] cycloaddition reactions with azomethines at the center C=C bond to give the cycloadducts 57 . 

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