Syntheses with perfluoroalkyl iodides. A review: Part III. Addition of RFI to norbornene esters, acids and anhydrides, alkenoic acids and esters, alkenylsuccinic anhydrides or diesters, and to vinyl monomers; lactonization and other reactions of adducts; hydroperfluoroalkylation by RFI; synthesis and reactions of I(CF2)nI homologues (n = 1–3); perfluoroalkylation of arenes by RFI or [RFCO2]2; RFI in the synthesis of RFSR

Abstract

RFI reacts with the endo cis dialkyl norbornene esters to give adducts in 95–100% yield; the RF radical adds to an exo position and RFI transfers iodine to an adjacent exo position. By contrast, RF adds exo and RFI transfers iodine endo to the endo- or exo-norbornenedicarboxylic anhydrides (Schemes 1–3 ). Exo-6-iodo ester 5a or 6a, when heated, eliminates RI and converts to a lactone (Scheme 4 ). Adduct 5a converts to nortricyclene 15a when treated with base. Alkenoic esters (or acids) add RFI to give adducts in high yield; the adducts lose alkyl iodide (or HI) and form lactones if the iodine is disposed at the γ- or δ-position (Scheme 5 ). Lactonization occurs during zinc reduction of the RFI adduct of allylsuccinic anhydride, or during RFI addition to highly branched dialkyl allylsuccinates (Schemes 6 and 7 ). Vinyl monomers differ in their response to RFI addition. Acrylates, acrylic acid and N,N′-dimethyl acrylamide add RFI to high conversion, instead of polymerizing, when irradiated with UV light of 454nm intensity. Induced by AIBN, acylamide reacts with RFI to give water soluble, unsaturated telomers of high surface activity. Extensive transfer to solvent occurs. Vinyl acetate (VAc) and RFI (azonitrile initiator) at 50°C give n-RFCH2CHIOAc (36) in 96% yield. Adduct 36 with AIBN adds VAc (in excess) stepwise to form telomers with n=2–8 (Scheme 8 ). RFI (in excess), VAc and AIBN (5mol%) at 80°C give 36, which is cleaved by a radical chain initiated by RF: 36⇄n-RFCH2CHO (38)+CH3C(O)I. RFI, with activated metals, hydroperfluoroalkylates alkenes (Scheme 9 ). Free radical chemistry of I(CF2)nI (n=1–3) has new significance in view of laser photolysis of the n=1 and n=2 congeners. I(CF2)1I (44) fragments to I2 and CF2: almost instantly. I(CF2)2I (54) loses first one I, and the ICF2CF2 radical loses the second I after 17 femtoseconds without rotating, to give CF2CF2 (Section 5.4.1). In 1962, 54 is found not to add to VAc with azo initiator, while Br(CF2)2I or Cl(CF2)2I adds readily; this behavior may be related to the lifetime of 54. The I(CF2)nI family (n=1–3) is synthesized in high yield by new methods. Peroxide, dithionite and metal oxidants initiate free radical reactions of ICF2I (44): 44 adds to methyl acrylate without polymerizing, and cyclohexene gives cis and trans adducts, 46a,b (Fig. 1 ). The trans-46 is diequatorial in conformation, analogous to cyclohexene trans-CF3I adducts (Section 5.2). With dithionite initiator, 44 gives mono- and bis-adducts from alkenes. With Pb(OAc)4, 44 adds to both ordinary and fluorine-substituted alkenes. Thus, ethene gives CF2(CH2CH2I)2 (86%), VF2 gives ICF2CH2CF2I (52; 92%), and TFE gives I(CF2)3I (53; 90%). Unlike its photolytic behavior, 44 is stable at 185°C for 30h, and adds thermally to ethene, propene, vinyl fluoride and certain vinyl ethers. At 185°C, ethene adds 44 to give mono adduct 55 (82%); VF2 gives 52 (83%) and TFE (mol=1:1) provides 53 and ICF2(CF2)4I (64) in 84% yield (53/64=12). Heating I2 with c-C3F6 (first prepared by adding CF2: to TFE at 155°C) gives 53 (80%). I(CF2)2I (54) adds thermally to TFE, and to ethene, to give versatile, reactive oligomers. Perfluoroalkylation of arenes by RFI (n-C4F9I) and benzoyl peroxide (BPO) in acetic acid gives n-C4F9IAr (70) in yields of 93–99% for benzene, anisole, diphenyl ether, toluene, biphenyl, naphthalene and thiophene. Conversions are 87–91%. Rearomatization of the RFArH radical is more efficient with BPO than with other systems (Scheme 12). Chlorobenzene, benzonitrile and nitrobenzene give 70 (41–47% yield) at 88% conversion (Section 7.1). Absolute rate constants (Table 7) and partial rate factors (Table 8) are reported. n-Perfluorobutylation of 1-octene with BPO and Cu(OAc)2 (Scheme 13) gives trans-n-C4F9CH2CHCHR (71, 83%), the cis isomer (72, 16%),and 1-(n-perfluorobutyl)-1-octene (73, 2%). Copper metal coupling of RFI and haloarenes, and other methods of 70 preparation are reviewed. Peroxides [(RFCO2)2] perfluoroalkylate arenes by an electron transfer from ArH to [(RFCO2)2] to give ArH+ and (RFCO2)2−, which fragments into RF, RFCO2− and CO2 (Scheme 16). Yields of 70 for RF=n-C3F7 or higher are 86–97%. RFI perfluoroalkylates thiols homolytically to give RFSR or RFSAr. Thiols RF(CH2)nSH (85) are synthesized from RFI (Scheme 17), and several methods are recently compared. Thiols 85 are being studied intensively in nanostructures, in self-assembled monolayers, and in many useful telomers or polymeric products.