Allenes carbene addition

High-temperalure carbene additions to allenes are especially prone to give rearranged methylenecyclopropanes [42, 43, 44] (equations 14 and 15), and there-... 

Another approach to substituted bicyclopropylidenes is by carbene addition onto butatrienes and alkenylidenecyclopropanes bringing the substituents in with the allene or with the carbene moiety as well as with both fragments. This way, Skattebol et al. [41] and later Kostikov et al. [42] have prepared tetrahalote-... 

Schemes. Carbene additions onto allenes as a synthetic approach to substituted bicyclopropylidenes (n.r. = yield not reported) [41-47]...

The cyclopropanation of alkenes with dihalocarbenes, CX2 or CX X, except for CF2, can be efficiently executed by the PTC procedures (CHX3/strong aqueous base/catalyst), which are well-documented in books and reviews . The dichloro- and dibromo-carbene additions by the PTC procedure have successfully been applied for many alkenes, conjugated polyolefins and allenes. Satisfactory results are also reported for the reactions of sterically hindered olefins as well as electronically deactivated olefins, which frequently... 

Arylcyclopropanes have also been prepared by metal-catalyzed carbene addition to 1,1-dimethylallene. When 4- and 3-nitrophenyldiazomethanes were decomposed with copper triflate in the presence of the allene, 2,2-dimethyl-3-methylene-l-(4-nitrophenyl)cyclopropane (7a) and 2,2-dimethyl-3-methylene-l-(3-nitrophenyl)cyclopropane (7b) were obtained in 62% and 38% yield, respectively. ... 

A novel synthesis of the lavandulyl skeleton depends on the hydrolysis of the spiro-compound (71), obtainable by a carbene addition on the allene (72). The resulting alcohol is converted into the bromide (73) from which isolavandulyl acetate (74) can be obtained. Allyl rearrangement of the bromide (73) during acetolysis and subsequent formation of the hydrocarbon (75), also mentioned in this paper, has been previously observed (c/ ref. 114). Photochemical sensitized oxygenation of lavandulyl acetate (76) is described it yields the expected products (77) and (78). ... 

What about a nucleophilic carbene, for which negative charge should build up on the olefinic carbon atoms during the carbene addition cf. 5 With ArCH=CH2 substrates, electron-withdrawing aryl substituents would stabilize such a transition state and the p value should be positive. There are several examples of this phenomenon. For example, cycloheptatrienylidene, 10, adds to / -substituted styrenes with p = -t-1.02 - 1.05 (vs. a) consistent with a nucleophilic selectivity that seems to implicate the aromatic resonance form 10a as an important feature of the carbene. [45] It is satisfying to compare this result with p = -0.76 (vs. a) or -0.46 (vs. a" ") for additions to styrenes of cyclopentadienylidene, 11, where contributions of the cyclopentadienide form (11a) would render the carbene electrophilic. [46] However, these conclusions are too facile. There is reason to believe that the chemistry attributed to 10 might in fact be due to its allenic isomer 12. [47] And the electronic structure of 11 is also more complicated than the simple depiction above. [48]... 

Cyclopropanations of alkenes with alkyl diazoacetates are catalysed by rhodium(ii) carboxylates, and Sasaki et al have shown that crown ethers have several advantages over quaternary ammoniurq ions for the catalytic synthesis of allene-cyclopropanes from addition of allene-carbenes to olehnic substrates. 

Terpenoid alkenylidenecyclopropanes of the type (10), which are easily synthesized by addition of the allene carbene (9) to various alkenes, have been found to be extremely useful intermediates in the synthesis of a range of functionalized head-to-tail and irregular monoterpenes (Scheme 2). ... 

Other potential synthetic routes to these unsaturated aziridine derivatives which involve the addition of nitrenes to allenes <75JOC224), carbenes to imines with subsequent hydrolysis <67JA362), and of carbenoid species to ketenimines <76TL1317,79TL559) have been investigated but are collectively of little or no preparative value. 

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. 

The addition of isocyanates (isoelectronic to CO) to group 14 carbene analogs was investigated in order to see if the resulting molecules w ould have an allene-like framework. In the first study, Wcidenbruch et attempted to synthesize... 

The earlier examples of [2 + 1] cycloaddition of a carbene (or carbenoid) on the double bond of alkylidenecyelopropanes to yield spiropentane derivatives were observed as undesired side reactions in the synthesis of alkylidenecyelopropanes through the addition of a carbene to a substituted allene [161]. In some cases the spiropentane derivative was obtained as the major product [161a, c] especially when a large excess of the carbene reagent was used. For example, when methyl 3,4-pentadienoate (610) was treated with a ten-fold excess of methylene iodide and zinc-copper couple the two products 611 and 612 were isolated in 1 4.5 ratio (Scheme 86) [161a]. 

The two-step process, depicted by path b, involves initial addition of the carbene carbon to an adjacent it bond to form bicyclo[4.1,0]hepta-2,4,6-triene (2a). This process has precedent in the analogous rearrangement of vinylcar-bene to cyclopropene (Scheme 6),lc18 and is supported by Gaspar s work on 1-cyclohexenylcarbene.17 In the second step of the mechanism in Scheme 5, subsequent six-electron electrocyclic ring opening of 2a yields the cyclic allene 3a. 

The discovery of carbene and carbenoid additions to olefins was the major breakthrough that initiated the tapping of this structural resource for synthetic purposes. Even so, designed applications of cyclopropane chemistry in total syntheses remain limited. Most revolve around electrophilic type reactions such as acid induced ring opening or solvolysis of cyclopropyl carbinyl alcohol derivatives. One notable application apart from these electrophilic reactions is the excellent synthesis of allenes from dibromocyclopropanes 2). 

This method has successfully been applied for the addition of chloro(l-chloro-2,2-dimethylvinyl)carbene — formed from 1,1,2-trichlo o-3,3-dimethylcyclopro-pane by dehydrochlorination and subsequent ring-opening — onto ketene methyl silyl acetals, the products of which are transformed to interesting allenic esters when treated with tetrabutylammonium fluoride [149]. 

When the carbene or carbenoid resulting from a dihalocyclopropane is unable to rearrange to the al-lene due to steric or other factors, insertion or addition reactions characteristic of carbenes take place. Thus dibromonorcarane on reaction with methyllithium gives a bicyclobutane derivative by insertion of the carbene into a 0-C—H bond (equation 57).178 Allene formation is sterically unfavorable in this case. Similarly, dibromotetramethylcyclopropane gives l,2,2-trimethylbicyclo[1.1.0]butane instead of tetra-methylallene (equation 58).179 181 An example involving a tricyclic dibromocyclopropane is given in equation (59).182... 

In a [4+2] cycloaddition reaction that proceeds via a Michael addition, an azadiene has been shown to react with Fischer carbenes yielding the 1,4-dihydropyridine after removal of the metal (Scheme 82) <1997TL3981>. Reactions of 1-azadienes with allenic esters yield the 1,4-dihydropyridine in excellent yield (Scheme 83) <20010L2133>. 

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