Diethylzinc—Methylene iodide

Methylidenation of allylic thioethers. Methylidenation of an allylic phenyl-thioether with methylene iodide-diethylzinc is accompanied by a 2,3-sigmatropic rearrangement to a homologous allylic phenylthioether. The rearrangement is also initiated by ethylidene iodide. Cyclopropanation is not observed. The Simmons-Smith reaction with allylic sulfides results only in formation of an insoluble polymer. 

Diethylzinc-Methylene iodide, i, 253 2, 134 4, 153. Diethylzinc is available from Aldrich and Alfa. 

The reaction of phenanthrene with zinc dust and methylene iodide in 1,2-dimethoxyethane gives 9,10-dihydro-9,10-methanophenanthrene (XIX) in 25% yield 408). The reaction of naphthalene with diethylzinc... 

Cyclopropaaalioa of olefins (I, 253 2. 134). Cyelopropanation of olefins with the diethylzinc-methylene iodide reagent is markedly accelerated by oxygen. In addition yields are improved. Thus the reaction of cyclohcxcnc with the carbenoid in the presence of air is complete within 30 min. norcaranc is obtained in 90 % yield. The yield is 53 % when the reaction is carried out under nitrogen. ... 

Recently it has been shown that cyclopropanone ketals and hemiketals can be prepared conveniently by cyclopropanation of ketene alkylsilyl ketals or ketene disilyl ketals with diethylzinc-methylene iodide in ether ... 

Diethylzinc, 1293 Diethylzinc-methylene iodide, 253 Difluoramine, 213, 253-254 Diiluoroaminobutanes, 1140... 

They later found that the disulfonamide-modified zinc complexes were much more effective catalysts. The reaction of several allyfic alcohols with diethylzinc and methylene iodide in the presence of differently substituted arylsulfona-mides derived ligands was examined in detail (Scheme 3). Although the p-trif-luoromethylbenzenesulfonamide catalyst (entry 5) facilitated the cyclopropana-tion of cinnamyl alcohol (2), the enantioselectivity observed was slightly lower than that observed with the o-nitro- or the p-nitrobenzenesulfonamide ligand (entries 2 and 4). Substitution at the meta-position resulted in a significant decrease of the enantioselectivity, probably due to steric reasons (entries 3 and 6). The cyclopropanation of (Zj-ciimamyl alcohol (3) and ( )-5-phenyl-2-penten-... 

Diethylzinc-Methylene iodide (Simmons-Smith reagent). 

Cyclopropanation of enol sttyl ethers. Cyclopropanation of these substrates with the Simmons-Smith reagent has been reported by several laboratories (4, 588-589). Cyclopropanation can also be effected with diethylzinc-methylene iodide in ether or in n-pentane under controlled conditions (70-80% yields). This reagent can also be used to convert cyclic enol silyl ethers (1) to spiro ethers... 

CYCLOPROPANATION Bis[(-)-camphor-quinone-a-dioximato] cobalt(II) hydrate. Diethylzinc-Methylene iodide. Rhodium(II) caiboxylates. 

Ring expansion induced by FeCla has been used in a new synthesis of dl-muscone in 237> overall yield from dimethyl tetradecanedioate, which was converted into (6) by the procedure of Ruhimann (4, 537). In this case cyclo-propanation with methylene iodide and diethylzinc (4, 153) proved superior to the Simmons-Smith reagent. ... 

The enormous potential provided by the Simmons-Smith reaction is further demonstrated in an efficient one-pot synthesis of spiro-compounds of the type (10) by reaction of cyclic enol-silyl ethers with diethylzinc-methylene iodide this remarkable synthesis ca. 70% overall) proceeds via the three sequential reactions (7) (8), (8) (9), and (9)— (10). The versatile dichlorocarbene species is most conveniently generated under phase-transfer conditions using either KOBu -crown or NaOH-PhCHzNEts Cl. 

The remaining new approaches to muscone all rely upon methods of ring expansion. Ferric chloride treatment of l,4-bis(trimethylsilyloxy)-bicyclo[12,l 0]pentadecane (155), obtained by cyclopropanation of the cyclotetradecene (154) with diethylzinc and methylene iodide, resulted in a one-carbon ring expansion to a muscone precursor, the dione (156). Anodic oxidation of the potassium salt of the /8-hydroxy-carboxylic acid (158), formed by Reformat-sky reaction of the enone (157), led, also by a one-carbon ring enlargement, to a mixture of the I3y- and a/8-unsaturated ketones (159) which was converted into... 

Zinc and Mercury.—As in previous years, reports of new transformations and methodologies involving zinc have been at a low level. A useful high-yielding conversion has been published, however, of allylic thioethers such as (84) into homoallylic thioethers (85). The initial ylide formation with a homogeneous solution of diethylzinc and methylene (R = H) or ethylidene (R = Me) iodide is followed by a 2,3-sigmatropic rearran ment to the observed products, and the poor yields found in previous experiments can be avoided by quenching the reaction mixture with acetaldehyde. Conventional Simmons-Smith cyclo-propanation of these compounds fails, as does the cyclopropanation of cyclohexene in the presence of various thioethers. 

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