6: 6-Biphenyl) [Cr(CO)3] 2 and (T)6:i)6-4,4'-dimethoxybiphenyl) [Cr(CO)3] 2 were chemically reduced with lithium anthracenide or lithium naphthalenide in THF to generate stable dianions having a (7j5-cyclohexadienylidene)2[Cr(CO)3]2 structure. The (j?5-cyclohexadienylidene)2[Cr(CO)3]2 dianion reacted cleanly with electrophiles such as H20, D20, benzyl tosylate, ally! tosylate, methyl iodide, and primary alkyl bromides, tosylates, and sulfates in a highly stereoselective and regioselective manner to form [M-6-substituted-6-(7j6-phenyl)(l-5-jj5)-cyclohexadienyl]bis(tricarbonyIchromium) anions. Direct oxidation of the [>i-6-alkyl-6-(i76-phenyl)(1-5-775)-cyclohexadienyl]bis(tricarbonylchromium) anions with iodine yielded 2-alkylbiphenyls, whereas protonation with trifluoroacetic acid (TFAA) generated [5-alkyl-5-(7?6-phenyl)-l,3-cyclohexadiene]tricarbonylchromiums. The [5-alkyl-5-(r;6-phenyl)-l,3-cyclohexadiene]tricarbonylchromiums were oxidized by I2 or air to generate the free 5-alkyl-5-phenyl-1,3-cyclohexadienes without rearrangement and in excellent yields. Chemical reduction of (j)6:t)6-4,4'-dimethoxybiphenyl)[Cr(CO)3]2 at -78 °C with lithium naphthalenide yielded a dianion which reacted with methyl triflate, ethyl triflate, or allyl tosylate. Workup with TFAA and I2 resulted in the formation of 4-alkyl-4-(4-methoxyphenyl)cyclohex-2-en-1 -one products in fair yields. Isolation of 4-al!yl-4-(4-methoxyphenyl)cyclohex-2-en-1 -one represents a formal synthesis of the synthetically important Sceletium alkaloid, O-methyljoubertiamine.be induced, generating the trans-5,6-disubstituted-cyclohexadiene,
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