Alkoxycarbonyl carbenes reactions

In connection with these catalytic cyclopropanation reactions, it should be mentioned that the isolable ruthenium-carbene complex 162, which is obtained from 19, [RuCMp-cymene)]2 and 2,6-bis(4-isopropyl-l,3-oxazolin-2-yl)pyridine, reacts with styrene at elevated temperature in a carbene transfer reaction83 (equation 41). Since complex 162 is also catalytically active for (alkoxycarbonyl)carbene transfer to olefins, this reaction represents one of the few connecting links between catalytic and stoichiometric carbene transfer reactions of metal-carbene complexes. 

The Simmons-Smith reaction seems to be of little value for transfer of an alkoxycarbonyl-carbene to alkenes. Thus, reaction of the reagent formed from ethyl diiodoacetate and zinc-copper couple with 2,5-dimethylhexa-2,4-diene (reflux, 14 days) furnished ethyl 2,2-dimethyl-3-(2-methylprop-l-enyl)cyclopropane-l-carboxylatein only 12% yield, and ethyl dichloroacetate was an even less suitable starting material. ... 

Addition of carbenoids derived from a-diazo carbonyl compounds to prostereogenic olefins can furnish two diastereomeric cyclopropane derivatives (dsjtrans- or euefo/exo-isomers). The metal-catalyzed transfer of alkoxycarbonyl carbenes has been closely investigated it usually furnishes the mwv-substituted cyclopropanes with moderate to good preference. The rhodium(II/-catalyzed reaction of ethyl diazoacetate with various olefins typically demonstrates that the d.r. (trans/cis) increases when the substituent on the olefin becomes sterically more demanding5. 

Nanaomycin A 103 and deoxyfrenolicin 108 are members of a group of naphthoquinone antibiotics based on the isochroman skeleton. The therapeutic potential of these natural products has attracted considerable attention, and different approaches towards their synthesis have been reported [65,66]. The key step in the total synthesis of racemic nanaomycin A 103 is the chemo-and regioselective benzannulation reaction of carbene complex 101 and allylacety-lene 100 to give allyl-substituted naphthoquinone 102 after oxidative workup in 52% yield [65] (Scheme 47). The allyl functionality is crucial for a subsequent intramolecular alkoxycarbonylation to build up the isochroman structure. However, modest yields and the long sequence required to introduce the... 

Rhodium(II) acetate was found to be much more superior to copper catalysts in catalyzing reactions between thiophenes and diazoesters or diazoketones 246 K The outcome of the reaction depends on the particular diazo compound 246> With /-butyl diazoacetate, high-yield cydopropanation takes place, yielding 6-eco-substituted thiabicyclohexene 262. Dimethyl or diethyl diazomalonate, upon Rh2(OAc)4-catalysis at room temperature, furnish stable thiophenium bis(alkoxycarbonyl)methanides 263, but exclusively the corresponding carbene dimer upon heating. In contrast, only 2-thienylmalonate (36 %) and carbene dimer were obtained upon heating the reactants for 8 days in the presence of Cul P(OEt)3. The Rh(II)-promoted ylide formation... 

Chromium carbene complexes, 82 Methyl acrylate, 183 (2R,4R)-Pentanediol, 237 Titanium(IV) chloride, 304 Nitroaldols Nitromethane, 199 Intramolecular reactions Methyl acrylate, 183 Other aldol-type reactions Bis(2-pyridinethiolato)tin(II), 40 Alkoxycarbonylation (see Carboalkoxy-lation)... 

The addition of carbenes and carbenoids to imines and nitriles continues to be a popular approach to aziridines and 2//-azirines. These processes have been well reviewed by Deyrup (B-83MI101-01). Dichlorocarbene and other dihalocarbenes have been added to a wide variety of imines to provide dihaloaziridines. A recent example is shown in Equation (64), illustrating the use of phase-transfer conditions <93H(36)69i). The treatment of azides with excess dichlorocarbene results in the formation of the 2,2,3,3-tetrachloroaziridines (92TL2339). Presumably, the azide is converted by dichlorocarbene to the imidoyl dihalide RN=CC12 which reacts further with dichlorocarbene. Transition metal-promoted reaction of a-diazoesters with imines provides 2-(alkoxycarbonyl)aziridines [Pg.46]

Due to the high reaction temperature and long reaction times, this method is less suited for the synthesis of thermally labile cyclopropanes. In such cases, the corresponding diazo esters are a better source of alkoxycarbonyl(chloro)carbene and alkoxycarbonyl(bromo)car-bene (see Section 1.2.1.2.4.2.6.2.). However, no alternative exists for transfer of alkoxycarbo-nyl(fluoro)carbenes here, [bromo(ethoxycarbonyl)fluoromethyl]phenylmercury is a more reactive precursor than [chloro(ethoxycarbonyl)fluoromethyl]phenylmercury. Typical examples are shown for the formation of 1, 2, and 3. Further examples are given in Houben-Weyl, Vol.E19b, pl044ff. 

Bis(camphorquinone-a-dioximato)cobalt(II) (10) has been developed as a catalyst for enan-tioselective cyclopropanation reactions. It allows selective carbene transfer from diazoacetic esters to terminal C-C double bonds which are in conjugation with vinyl, aryl, alkoxycarbonyl or cyano groups, but not to alkyl-substituted alkenes, cycloalkenes, 1,3-dienes and al-lenes. The unusual chemoselectivity and some other experimental observations make the two mechanistic pathways proposed vide supra) questionable for these special carbene-transfer reactions. In contrast, the cobalt(II) complex 11 allows not only the cyclopropanation of styrene but also of oct-l-ene, a nonactivated alkene (ethyl diazoacetate, 35 °C, 3mol% of catalyst yield 50-60%). ... 

Phosphorylglycines are easily prepared, but in limited yield, by alkoxycarbonylation of the a-lithiated Schiff base of diethyl aminomethylphosphonate in THF at low temperature. The acylated Schiff base is converted in high yield (80%) to the corresponding p-lactam by photochemical reaction with the [(methoxy)(methyl)carbene]chromium complexes in CHjCF. ... 

Ethoxycarbonylnitrene (generated photochemically from the azide) also reacts with 4-t-butylthian, affording a nearly 1 1 mixture of both cis- and trans-sulphimides. This non-stereoselectivity in the reaction of the nitrene is in marked contrast with that of the reaction of carbenes with the thian the thian reacts with both bis(alkoxycarbonyl)- and bis(diacetyl)-carbenes, giving the trans-yMes as the sole products (see Vol. 4, p. 112). Various sulphimides of cyclic sulphides, e.g. thians, cis- and frans-thiadecalins, oxathians, and dithians, can be prepared by treating the sulphides either with anilines and AT-chlorosuccinimide or with Bu OCl. In this reaction, the formation of (33 R = Bu , = /7-ClCjH4) with an equatorial... 

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