Nucleophilic reactions, fluorinated dienes

Fluorinated dienes, like fluoroalkenes, are very susceptible to nucleophilic attack [90, 91] some examples of nucleophilic substitution processes are given in Table 7.17. Examples of rearrangements and other reactions are also listed. An early demonstration that... 

The [4+1] cycloadducts formed from 4,4-bis(trifluoromethyl)-l-oxa-buta-1,3-dienes (92JPR219) and tin(II )-chloride are transformed on heating into 4,4-difluoro-3-trifluoromethylbut-3-en-l-ones, which on treatment with sodium hydride yield 2-fluoro-3-trifluoromethylfurans (92CC348). When heated with phosphorus pentasulfide, l-aryl-4,4-difluoro-3-trifluor-omethylbut-3-en-l-ones give 2-fluoro-3-trifluoromethylthiophenes. The fluorine atom at C—2 of the furans and thiophenes can readily be substituted by a wide variety of nucleophiles (92JPR3II). This reaction sequence represents a preparatively useful method for the selective introduction of biologically relevant substituents into the C—2 position of 3-trifluoro-methyl-substituted furans and thiophenes (Scheme 87). 

The acetoxy group was hydrolyzed using hydrazine to give (46). Nucleophilic substitution of the fluorine atom produced the tricyclic /3 lactam (47). A diastereoselective aza-Diels-Alder reaction was used in a synthesis of (-)-lasubine (I). Tin tetrachloride mediated reaction of complex (48) with Danishefsky s diene afford 2,3-dihydro-4-pyridone (49) as a single diastereomer (Scheme 86). Chiral benzaldehyde imines can be aUylated with high diastereoselectivity to give optically active homoaUyhc amines (Scheme 87). 

Model compound studies reveal factors which influence free—radical additions of ethers, polyethers, and crown—polyethers, to fluorinated alkenes. Stereo-electronic effects significantly affect relative reactivities of cyclic amines. Novel dienes are obtained by reactions of some oligomers of fluorinated alkenes with sodium amalgam and some reactions of these systems with nucleophiles are described. 

Most reports concerning 2//-pyran-2-ones (a-pyrones) involve non-fluorinated derivatives, which perform important biological functions in nature and have unlimited synthetic potential for the construction of a variety of arenes and heteroarenes [28], However, very few deal with 2-pyrones containing fluoroalkyl groups. It is evident that the C-2, C-4 and C-6 positions of the 2-pyranone ring are electrophilic in nature and prone to nucleophilic attack. The presence of polyfluoroalkyl substituents on the pyrone ring favours these reactions. At the same time, R -containing 2-pyrones behave as cyclic dienes in cycloadditions. 

Gyclic and acyclic [(pentadienyl)Ee(GO)2L]X complexes (L = GO, PPh3) react with nucleophiles to form the corresponding complexes containing terminal acyloxy or alkoxy substituents.The synthesis of the first (diene)Ee(GO)3 complex functionalized with a fluorine atom in the allylic position has been reported.Reactions... 

Reaction of 1,4-dilithio-l,3-dienes 1 with 1.1 or 1.2 equiv of CeFe at room temperature afforded the multi-substituted partially fluorinated naphthalene derivatives 2/6 in good to high isolated yields (Scheme 12) [56]. The reaction is assumed to proceed via double nucleophilic substitution. The naphthalene derivatives with different substitution patterns could be prepared conveniently by this method. Instead of nucleophilic substitution, when di-lithio reagents 1 were treated with hexachlorobenzene, chloropentafluorobenzene, or bromopentafluorobenzene, chlorine-lithium or bromine-lithium exchange reactions took place to afford the 1,4-dichloro- or 1,4-dibromo-l,3-diene derivatives. Preliminary results demonstrate that these partially fluorinated multi-substituted naphthalene derivatives show unique stacking fashions. 

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