Intermolecular double-bond insertion

The palladium-catalyzed domino assembly of norbornene (65), the ds-alkenyl iodide 66, and a terminal alkyne or cyanide reported by Torii, Okumoto et al. [315] provides an example for a sequence of oxidative addition, intermolecular double bond insertion, and interception of a copper acetylide or potassium cyanide. These reactions with acetylenes have been performed in good yields in the presence of diethylamine, tetra-n-butylammonium chloride, and catalytic amounts of palladium acetate, triphenylphosphine, and copper] I) iodide. Remarkably, they are characterized by complete inversion of the cis configuration of the alkenyl iodide and a high degree of discrimination for the enantiotopic ends of the double bond in norbornene. To account for that, intermediate formation of a cyclopropylcarbinyl-palladium species by a 3-exo-trig cyclization in 67 and subsequent cycloreversion to a new homoallylpalladium intermediate as the direct precursor to 68 and 69 has been assumed. Thus, the products 68 and 69 are formed virtually with complete stereoselectivity (Scheme 8.17). 

The benzene derivative 409 is synthesized by the Pd-catalyzed reaction of the haloenyne 407 with alkynes. The intramolecular insertion of the internal alkyne, followed by the intermolecular coupling of the terminal alkyne using Pd(OAc)2, Ph3P, and Cul, affords the dienyne system 408, which cyclizes to the aromatic ring 409[281]. A similar cyclization of 410 with the terminal alkyne 411 to form benzene derivatives 412 and 413 without using Cul is explained by the successive intermolecular and intramolecuar insertions of the two triple bonds and the double bond[282]. The angularly bisannulated benzene derivative 415 is formed in one step by a totally intramolecular version of polycycli-zation of bromoenediyne 414[283,284],... 

A similar but different mechanism has also been proposed for the intermolecular CO-SiCaC reaction of phenylacetylene catalyzed by Rh4(CO)i2, which gives silylcyclo-pentenone 9a and 9b (Scheme 7.5) [14]. In this mechanism /9-silylethenyl-[Rh] intermediate Il.lg, arising from insertion of the alkyne moiety into the Si-[Rh] bond, reacts sequentially with a second molecule of phenylacetylene and CO, to afford <5-silylpenta-dienoyl-[Rh] complex II. Ih- Finally, carbocyclization followed by double-bond migration gives 9 a and 9 b. 

Carbenes and carbenoids can add to double bonds to form cyclopropanes or insert into C—H bonds. These reactions have very low activation energies when the intermediate is a free carbene. Intermolecular insertion reactions are inherently nonselective. The course of intramolecular reactions is frequently controlled by the proximity of the reacting groups.53... 

The intermolecular carbopalladation of a triple bond can be faster than that of an intramolecular double bond as, for example, in the (9-iodo(l-methylallyl)benzene 152. The arylpalladium iodide initially formed from 152 and a palladium(O) species intermolecularly carbopalladates diphenylacetylene 71, and only the thus formed alkenylpalla-dium intermediate 153 undergoes insertion into the internal double bond to furnish the neopentylpalladium species 154 which, by <9r/ (9-attack on the adjacent phenyl group, finally forms the tetracyclic system 155. ... 

With its (9r/ (9-(cu-phenylalkynyl) group, the iodoarene 156 in the presence of a palladium catalyst initiates the cascade process with an intramolecular carbopalladation this is followed by an intermolecular insertion, for example, into the double bond of the 3-azanorborn-5-en-l-one 157 and terminated by ortho-2XX,2Jz of the norbornyl-type cr-palladium intermediate on the previously terminal aryl group to yield the two regioisomeric hexacyclic systems 158 and 159 in a ratio of 1 1 (Scheme 39). ... 

As mentioned previously, the partially reduced forms of five membered heteroaromatic systems might act as olefins in insertion reactions. This behaviour is characteristic particularly of dihydrofuranes. The olefin insertion and the following / hydride elimination should in principle lead to a trisubstituted olefin, which is rarely observed, however. Typical products of this reaction are 2-aryl-2,3-dihydrofuranes. A characteristic example of such a reaction is presented in 6.54. The coupling of 4-iodoanisole and dihydrofurane led to the formation of the chiral 2-anisyl-2,3-dihydrofurane in excellent yield.83 The shift of the double bond, which leads to the creation of a new centre of chirality in the molecule, opens up the way for enantioselective transformations. Both intermolecular and intramolecular variants of the asymmetric Heck reaction have been studied extensively.84... 

Analysis of the product distributions arising from both sensitized and non-sensitized irradiation of 2-allyloxyphenyldiazo species (8) showed that the C—H insertion product and much of the cyclopropanation arise from the triplet carbene.16 For the singlet carbene, intermolecular 0—H insertion with methanol is about 50 tunes faster than intramolecular addition to the double bond, hi this system, intramolecular reactions and intersystem crossing of the triplet carbene proceed at similar rates, hi the closely related indanyl system (9), the smaller RCR angle stabilizes the singlet state relative to the triplet and the intramolecular reactivity is dominated by the singlet state.17... 

Oxidative cyclization is another type of oxidative addition without bond cleavage. Two molecules of ethylene undergo transition metal-catalysed addition. The intermolecular reaction is initiated by 7i-complexation of the two double bonds, followed by cyclization to form the metallacyclopentane 12. This is called oxidative cyclization. The oxidative cyclization of the a,co-diene 13 affords the metallacyclopentane 14, which undergoes further transformations. Similarly, the oxidative cyclization of the a,co-enyne 15 affords the metallacyclopentene 16. Formation of the five-membered ring 18 occurs stepwise (12, 14 and 16 likewise) and can be understood by the formation of the metallacyclopropene or metallacyclopropane 17. Then the insertion of alkyne or alkene to the three-membered ring 17 produces the metallacyclopentadiene or metallacyclopentane 18. 

In the construction of the conjugated triene system 177 in vitamin D, the intermolecular insertion of the terminal triple bond of the 1,7-enyne 175 to the alkenylpalladium, formed from 174, occurs at first to form the alkenylpalladium 176. Further intramolecular insertion of the terminal double bond in 176, followed by fi-elimination yielded the triene system 177 in 76% yield [77]. 

Intermolecular insertion of alkenes to a-allyl intermediates is possible with an Ru catalyst. For example, 3,5-dienecarboxamide 274 is formed in high yield by Ru(cod)(cot)-catalysed coupling of 2-butenyl methyl carbonate (273) with acrylamide in the presence of A-methylpiperidine [122], Ni-catalysed transformation of allyl 3-butenoate (275) to heptadienoic acids 276a and 276b proceeds by insertion of the double bond to 7r-allylnickel intermediate [123],... 

Since alkyl- and dialkylcarbenes undergo rapid intramolecular insertion into a- and jS-C-H bonds, the intermolecular addition of these species to olefinic double bonds is not practical (Sections II.B, Merely, the intramolecular reactions produce three-... 

Coupling of a Fischer carbene complex with an alkene can generate a vinylcarbene intermediate 12 via an insertion-rearrangement reaction, which can then further react with a double bond. For intramolecular reactions of tethered enynes 10, the products formed are bicyclic cyclopropanes 14 intermolecular reactions lead to cycloalkenylcyclopropanes. 

The intermolecular variant of the O-H insertion reaction gets stuck at the stage of the initial adduct 8. We envisioned that if R1 = allyl, coordination of the double bond to the metal would initiate a Claisen-type process to form the jr-allylruthenium complex 9, whose reductive elimination would form the allyl ketone starting from terminal alkynes and allyl alcohols (Equation 1.10). Gratifyingly, this prediction was fully realized as shown in Equation 1.11 [13]. A tertiary ester does not undergo elimination under these reaction conditions (Equation 1.12). Dihydroxylationofthe double bond and subsequent acidification effect cyclodehydration to form furans in two overall steps. Subsequent elimination of the elements of acetic acid completes a synthesis of rosefuran 10, one of the most prized fragrances [14]. 

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