3- iodo-2-cyclohexen-l-one

Lithium (phenylthiocyclopropylcuprate) 185, prepared by the reaction of cuprous thiophenolate with cyclopropyllithium in THF at —78 °C, was added to p-iodo-enones. For example, treatment with 3-iodo-2-cyclohexen-l-one 186 provided the corresponding P-cyclopropyl a,P-unsaturated ketones 187 with high efficiency, Eq. (59) 127). 

Cuprate methodology can also be used to prepare more highly substituted substrates. Thus, treatment of the 3-iodo-2-cyclohexen-l-ones (82) and (84) with the epimeric, stereochemically homogeneous cuprates (89) and (90) produces the divinylcyclopropanes (91> 94) in excellent yields (equation (4). ... 

The overall reaction makes it possible to perform intramolecular caibozincations [65-71] via a radical cyclization. This useful preparation of cyclopentylmethylzinc derivatives proceeds with excellent stereoselectivity and allows preparation of quaternary centers. After cyclization, the zinc organometallic can be transmetallated with CuCN-2LiCl and made to react with a broad range of electrophiles such as acid chlorides, allylic and alkynyl halides, ethyl propiolate, 3-iodo-2-cyclohexen-l-one, and nitroolefins such as nitrostyrene, leading to products of type 40 (see Section 9.6.9 Scheme 9-34) [65,70]. 

The extension of this cross-coupling to iodoalkenes is also possible. If the iodo-, bromo-, or chloroalkene is further conjugated with an electron-withdrawing group, a facile substitution via an addition-elimination mechanism is observed. Typically, 3-iodo-2-cyclohexen-l-one 24 [55] reacts with a zinc-copper reagent such as 25 furnishing the expected cross-coupling product 26 (see Section 9.6.5 Scheme 25) [13]. 

A unique system for catalytic silaboration of allenes, in which a catalytic amount of organic halide is used as a crucial additive, has been reported (Equation (86)).232 In the presence of Pd2(dba)3 (5 mol%) with 3-iodo-2-methyl-2-cyclohexen-l-one (10mol%), reactions of terminal allenes with a silylborane afford /3-silylallylboranes in good yields with excellent regioselectivity. It is worth noting that the addition takes place at the terminal C=C bond in contrast to the above-mentioned palladium-catalyzed silaboration. The alkenyl iodide can be replaced with iodine or trimethylsilyl iodide. The key reaction intermediate seems to be silylpalladium(n) iodide, which promotes the insertion of allenes with Si-C bond formation at the central -carbon. 

B. 2-(4-Methoxyphenyl)-2-cyclohexen-1-one. A 500-mL, round-bottomed flask, equipped with a 1.5-in. Teflon-coated magnetic stirring bar and an argon inlet adaptor, is charged with 10.02 g (45.1 mmol) of 2-iodo-2-cyclohexen-1-one, 10.69 g (70.4 mmol, 1.56 eq) of 4-methoxyphenylboronic acid (Note 8), 16.72 g (72.1 mmol, 1.6 eq) of silver(l) oxide (Ag20) (Note 9), 0.85 g (2.8 mmol, 6 mol %) of triphenylarsine (Note 10), 0.53 g (1.4 mmol, 3 mol %) of palladium(ll) bis(benzonitrile)dichloride (Note 11), 200 mL of tetrahydrofuran (THF) and 25 mL of water (Note 12). The reaction mixture, flushed with argon, is stirred for 1 hr and then quenched by the addition of 125 mL of saturated aqueous ammonium chloride. After the solution is stirred for 1 hr, the... 

Some ylides from cyclic precursors are thermally labile and isomerize to iodo-enol ethers for example, the ylide of dimedone afforded 2-iodo-3-phenoxy-5,5-dimethyl-2-cyclohexanone [41], A similar reaction involving cleavage of the I-Cphenyi bond occurred with triethylphosphite 2-iodo-3-ethoxy-5,5-dimethyl-2-cyclohexen-l-one was the main product (65%) [42],... 

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