Dihydropyrroles cyclopropanation

A novel soluble complex, (t/ -ethene)hydrotris(3,5-dimethylpyrazol-l-yl)boratocopper(I) (3) mediates the cyclopropanation of styrene, hex-1 -ene, and cyclooctene with ethyl diazoacetate in 76 96% yield (25 C, 1 mol% of catalyst).Copper complexes with the tridentate 2,6-bis[(5-oxo-2,5-dihydropyrrol-2-ylidene)methyl]pyridine ligand or homologous tetradentate l,T-bipyridine and l,T-biisoquinoline ligands are also suited to cyclopropanation of styrene with ethyl diazoacetate. 

A .A -Dialkyl enamines yield alkyl 2-dialkylaminocyclopropane-l-carboxylates in low yield only, or, more typically, not at all. In contrast, less nucleophilic enamines, such as 77-acyl enamines (see Houben-Weyl, Vol. El9b, p 1153), A-acyl-2,3-dihydropyrroles, 77-acyl-l,2,3,4-tetrahydropyridines and A W-bis(trimethylsilyl) enamine 15, are cyclopropanated by diazoacetic esters without problems, e.g. formation of 16. In contrast to ( )-15, the Z-isomer and related trisubstituted enamines are cyclopropanated only in low yield (5-10%). ... 

Carbenoid attack at the heteroatom of allylic halides, ethers, amines, sulfides, and selenides generates an allylic ylide 23 that can undergo [2,3] sigmatropic rearrangement and, less frequently, [1,2] insertion (C-X insertion with and without allylic rearrangement, respectively). Similarly, an Af-acyl-2,5-dihydropyrrole could be cyclopropanated with ethyl diazoacetate in good yield. 

Cyclopropylphosphine oxides (140) react with the sodium salts of amides, presumably via cyclopropane ring-opening and intramolecular olefination, to give dihydropyrrole derivatives in moderate to good yield. Vicarious nucleophilic substitution reactions of a variety of substituted nitrobenzene derivatives with the carbanion of chloromethyldiphenylphosphine oxide to give o-(141) and p-(142)-nitrobenzyldiphenylphosphine oxides have been investigated. ... 

The cyclopropane substructure in the N-protected dihydropyrrole derivative 523 collapses after the cyclization and delivers a highly functionalized product 525 (Scheme 13.118) [208]. 

Beginning in 1998, Ma has developed a series of cascade cross-coupling cycliza-tion reactions of functionalized allenes with organic hahde in the presence of palladium species, leading to various highly substituted carbocycles or heterocycles, such as y-butenolides, y-lactams, y-iminolactones, vinylic epoxides, 2,5-dihydrofurans, 2,3-dihydropyrroles, furans, vinylic cyclopropanes, and cyclopentenes, which depend on the nature of the functional groups and the substituents on the allenes. This has been well summarized by the author [102] (Scheme 6.76). 

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