Cycloprop anation

The cycloprop anation of fulvenes has been effected with alkynylcarbene complexes (see Sect. 2.1.1). However, this reaction is inhibited in the presence of CO and under these conditions a formal [4S+3C] cycloadduct is formed [15a]... 

The reaction of alkenylcarbene complexes and alkynes in the presence of Ni(0) leads to cycloheptatriene derivatives in a process which can be considered as a [3C+2S+2S] cycloaddition reaction [125]. As shown in Scheme 77, two molecules of the alkyne and one molecule of the carbene complex are involved in the formation of the cycloheptatriene. This reaction is supposed to proceed through the initial formation of a nickel alkenylcarbene complex. A subsequent double regioselective alkyne insertion produces a new nickel carbene complex, which evolves by an intramolecular cycloprop anation reaction to form a nor-caradiene intermediate. These species easily isomerise to the observed cycloheptatriene derivatives (Scheme 77). 

For intramolecular cycloprop anation of simple 1,3-carbodienes with acyloxycarbene complexes see reference [13a]... 

Keywords Cycloprop anation Insertion Ylide reactions Asymmetric catalysis Synthesis... 

The addition of different types of carbenes onto bicyclopropylidene (1) is a common method for the preparation of [3]triangulane derivatives as well as branched trianguianes and normally proceeds without complications (for a review see [77]). Thus, the cyclopropanation under Gaspar-Roth [60] or modified Simmons-Smith [111] conditions gave dispiro[2.0.2.1]heptane ([3]triangulane, 97) in 80 [105] and 15% yield [5], respectively (Scheme 23). The palladium(II) acetate-catalyzed cycloprop anation of 1 with diazomethane, however, gave a number of products resulting from insertion of one or more than one methylene units into an initially formed palladacyclobutane 115 [112,113] (Scheme 23). 

Trimethylamine N-oxide, 325 Vinyltrimethylsilane, 343 Other reactions (Phenylsulfonyl)allene, 247 Cyclodehydration Diethoxytriphenylphosphorane, 109 Hexamethylphosphoric triamide, 142 Cycloprop anation Simmons-Smith reaction Diiodomethane-Diethylzinc, 276 Simmons-Smith reagent, 275 by other reagents which add CH2 to a carbon-carbon multiple bond Dibromomethane-Zinc-Copper(I) chloride, 93... 

Besides the 1,3-dipolar cycloaddition of azomethine ylides to C60, the Bingel cycloprop anation reaction is widely used for regioselective functionalization of fullerenes. In principle, this versatile modification involves the generation of carbon nucleophiles from a-halo esters and their subsequent addition to C60 [19]. The addition takes place exclusively on double bonds between two six-membered rings of the fullerene skeleton, yielding methanofullerenes. As shown in Scheme 2, addition of diethylbromomalonate to C60, in the presence of an auxiliary base... 

Silyloxycyclopropanes, which are readily available by cyclopropanation of si-lyl enol ethers, are versatile intermediates in organic synthesis. Reiflig, who has developed this chemistry, has studied enantioselective cycloprop anations of si-lyl enol ethers systematically [59]. The products which can be obtained from si-lyloxycyclopentene and diazoacetates in optically active form can be converted... 

The absolute configuration of the cyclopentyl phenylacetate (R=H) produced by the S-isomer of the catalyst, was established as R by analogy, the other C-H insertion products were presumed to be R. A transition state model similar to that proposed for asymmetric cycloprop anation with the same catalyst was used to interpret the asymmetric induction observed in C-H insertion. The rhodium carbene complex is represented as in Fig. 12 with the catalyst presumed to be-... 

Furthermore, Denmark has carried out the catalytic and enantioselective cycloprop anation of a broad range of allylic alcohols and one homoallylic alcohol... 

Based on a most simple analysis, one might approach the design of a metal-im-ido transfer catalyst by considering the corresponding reactivity of metal-carbe-noid complexes or metal-oxo complexes (Fig. 2). It is interesting, in fact, that all of the imido transfer catalysts identified thus far fall into the general category of olefin epoxidation or cycloprop anation catalysts. 

The products of these cycloprop)anations retain any cis or trans stereochemistry of the... 

Lundurine A could be synthesized from indoloazocine TTT-12 after cycloprop-anation of the indole ring. The intermediate III-12 would be formed by gold(III)-catalyzed cyclization of the alkynylindole ni-13, (See Ref. [118] and [133] in Chap. 1) which arises from III-14 upon conversion of the ester group into a homologated alkyne." Compound III-14 would be assembled from an enantiome-rically pure pyroglutamic ester derivative III-16 and an indole derivative III-15. Two approaches were considered for the cyclopropanation reaction from TTT-12 derivatives (Scheme 4.12) the intermolecular (A) and intramolecular (B). 

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