Carbenes insertion, into

The cyclohexylpyrazole (376) and the azlrlne (377) are formed by irradiation of 3-dlazo-4-methyl-5-phenylpyrazolenine (378) in cyclohexane (Scheme 35) (77JA633). The former is the result of carbene insertion into cyclohexane followed by a [1,5] hydrogen shift, whereas the latter arises by ring cleavage of nltrene (379) or by a concerted pathway. 

In another experiment tritiated adamantane diazirine fixed to the hydrocarbon core of a membrane gave rise to carbene insertion into the catalytic subunit of ATP-ase. After protolytic degradation adjacent areas of the original structure became evident (80JBC(255)860). 

An attempt to measure the IR spectrum of the hydroxy carbene [28] after UV photolysis (A>220 nm) of formaldehyde isolated in an argon matrix was unsuccessful (Sodeau and Lee, 1978). Instead of [28] only hydroxyacetal-dehyde resulting from carbene insertion into the C—H bond of the starting formaldehyde was found in the reaction products. Due to its small size, the... 

The interaction between catalyst and diazo compound may be initialized by electrophilic attack of the catalyst metal at the diazo carbon, with simultaneous or subsequent loss of N2, whereupon a metal-carbene complex (415) or the product of carbene insertion into a metal/ligand bond (416) or its ionic equivalent (417) are formed. This is outlined in a simplified manner in Scheme 43, which does not speculate on the kinetics of such a sequence, nor on the possible interconversion of 415 and 416/417 or the primarily formed Lewis acid — Lewis base adducts. 

The Lewis acid-Lewis base interaction outlined in Scheme 43 also explains the formation of alkylrhodium complexes 414 from iodorhodium(III) meso-tetraphenyl-porphyrin 409 and various diazo compounds (Scheme 42)398), It seems reasonable to assume that intermediates 418 or 419 (corresponding to 415 and 417 in Scheme 43) are trapped by an added nucleophile in the reaction with ethyl diazoacetate, and that similar intermediates, by proton loss, give rise to vinylrhodium complexes from ethyl 2-diazopropionate or dimethyl diazosuccinate. As the rhodium porphyrin 409 is also an efficient catalyst for cyclopropanation of olefins with ethyl diazoacetate 87,1°°), stj bene formation from aryl diazomethanes 358 and carbene insertion into aliphatic C—H bonds 287, intermediates 418 or 419 are likely to be part of the mechanistic scheme of these reactions, too. 

Carbene 103 undergoes 1,3-CH insertion to nortricyclene (105), but this reaction is either too rapid for LFP measurement by the pyridine ylide method (r <0.1 ns), or the insertion occurs by RIES of the precursor 2-norbomyldiazirine. Theoretically, a short lifetime is expected for 103 AG for the carbene insertion into the 6-endo-CU bond (103 — 105) is computed at 5.2 kcal/mol, about 6.7 kcal/mol less than the (unobserved) exo- 1,2-H shift to norbomene.16... 

II. Regioselectivity of the Carbene Insertion into a C-H Bonds of Alkoxides. 289... 

II. REGIOSELECTIVITY OF THE CARBENE INSERTION INTO a C-H BONDS OF ALKOXIDES... 

Acyclic and cyclic allylic ethers and acetals react normally with dihalocarbenes at the C=C bond [e.g. 77, 85, 108,114,121,122], Carbene insertion into the C=C bond of allylic ketones, which can be complicated by competitive reaction by the carbonyl group, can also be effected via the initial formation of the acetal and has been used in the synthesis of cyclonona-3,4- and -4,5-dienones from cyclooctenones [125],... 

Carbenes insert into the N=N bond of azo compounds and the unstable adducts rearrange spontaneously to produce benzopyrazoles (e.g. Scheme 7.31) [37,38], The reactions of azo compounds with dichlorocarbene is also catalysed by tertiary amines [36] and, under such conditions, azoxyarenes produce the benzimidazoles, presum-... 

Like carbene insertions into carbon-hydrogen bonds, metal nitrene insertions occur in both intermolecular and intramolecular reactions.For intermole-cular reactions, a manganese(III) meio-tetrakis(pentafluorophenyl)porphyrm complex gives high product yields and turnovers up to 2600 amidations could be effected directly with amides using PhI(OAc)2 (Eq. 51). The most exciting development in intramolecular C—H reactions thus far has been the oxidative cychzation of sulfamate esters (e.g., Eq. 52), as well as carbamates (to oxazolidin-2-ones), ° and one can expect further developments that are of synthetic... 

Shift of sulfonium ylide has been applied in organic synthesis as a useful methodology for carbene insertion into a G-S bond. This reaction has been particularly applied in the synthesis of cyclic thioethers, as shown in Equation (19)." " ... 

Early1 examples for this type of reaction were reported by Negishi and coworkers in the late 1980s2. a-Haloorganolithium carbenoids 4 were shown to react with a large variety of organometallics LmMR 3 to give the products of a formal carbene insertion into the metal-carbon bond (5) after hydrolysis (equation 2). 

Usually, carbon-carbon bonds are formed by coupling two carbons each of which are already functionalized in some way, as with the displacement of a C-Br with NaCN to form C-CN. It would be more efficient, and potentially less expensive and less polluting, if one of the partners could be an ordinary C-H bond. Intramolecular processes for carbene insertion into unactivated C-H bonds have been known for years. Practical intermolecular processes for C-C bond formation to a C-H bond are just starting to appear. 

Carbene insertion into a metal-hydrogen bond gives a methyl group that can undergo curbene insertion in a propagating manner H... 

This process has found occasional use in the synthesis of heterocycles. The major product resulting from the reaction of MeLi on the dibromocarbene adduct (51) is the tetrahydrofuran (52), as shown in equation (105).189 In a novel approach to the synthesis of spiroacetal pheromones, caibene insertion into an acetal C—H bond was studied (equation 106).252 Unfortunately, the reaction proceeds in low yield and the approach is further hampered by the lack of stereocontrol in the ring opening of the cyclopropane. Carbene insertions into N—H and C—H bonds adjacent to nitrogen have been shown to give azabicyclo systems, as shown in equations (107) and (108).188... 

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