Regioselectivity of the Reactions of Heteroatom-Stabilized Allyl ...

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700 Scheme 123 Scheme 124 E. Nitrogen and Phosphorus 1. 1-(Diethoxyphosphoryl)-1-(dimethylamino)-1-propenes (C−CdC(NMe2)(PO(OEt)2) 1-(Diethoxyphosphoryl)-1-(dimethylamino)allyl anion 674 undergoes γ-alkylation and silylation to give 675 which can be alkylated again to give 678, 680, and 682 and yield upon hydrolysis the corresponding carboxylic acid 679, 681, and 683 alkylated at C-3. Reaction with benzaldehyde gives low yields of the δ-hydroxyallyl compound 677, similar to the reaction with isobutenoxide producing 676 (Scheme 125). 354 F. General Discussion The orientation of reactions with electrophiles of allyl anions stabilized by two different gem-heteroatoms are summarized in Scheme 126. Geminal benzotriazole/alkoxy substituents (Bt-C- OR) direct substitution exclusively to the R-position for all electrophiles studied except very sterically crowed carbonyl groups where the regioselectivity favors γ-substitution. A rather similar pattern is shown for cyano/alkoxy (NC-C-OR) except that here reactions with carbonyl electrophiles are probably reversible and kinetically favor R-substition at low temperature but thermodynamically favor γ-substitution at high temperature. For cyano/diallylamino (NC-C-NR2), conjugate addition occurs R but allylation gives R/γ mixtures. Another set of geminal substituents shows essentially exclusive reaction at the γ-position. This includes P(O)R2 or PO(OEt)2 paired with OMe, OSiMe3, NR2, and SiMe3. The SiMe3/SR pair also Scheme 125 belongs this class as does the ionized N-triazolyl/ ethoxy derivative. The SiR3/Cl and SiR3/OR pairs fall into an intermediate position showing a mixture of R- and γ-substitution. V. Allyl Anions Stabilized by Two Non-Gem- Heteroatoms (XCdC−CY and CdCX−C−Y) In addition to allyl anions stabilized by two identical heteroatoms, allylic systems bearing two different heteroatoms have been studied particularly those containing oxygen or sulfur. A. Two Identical Heteroatoms Symmetrical allylic systems substituted in the 1and 3-position by two identical heteroatom-linked substituents are a unique class of compounds, since attachment of an electrophile to either terminal carbon yields the same product. We also discuss compounds 1,3-disubstituted by two different functional groups linked by the same heteroatom. 1. 1,3-Bis(alkylthio)-1-propenes (RS−CdC−C−SR) The 1,3-bis(methylthio)allyl anion is readily synthesized in a three-step sequence from epichlorhydrin. Although probably intrinsically unstable, it undergoes a clean reaction with electrophiles to give a protected form of the conjugated aldehyde RCHd
Scheme 126. Two Different Gem-Heteroatoms CHCHO. 355,356 In the case of unsymmetrically substituted anions 684 with different steric requirements at the 1- and 3-allylic carbon atoms, the least hindered of these will be the most readily alkylated to give predominantly 685 (Scheme 127). 357 Oshima et al. 358 carried out the same reactions but used transmetalation with CuI. Scheme 127 2. 1,3-(Diphenylseleno)-1-propene (PhSe−CdC−C−SePh) 1,3-(Diphenylseleno)propene 687 after metalation reacts smoothly with alkyl halides, TMSCl, epoxides, and carbonyl compounds. The products 688 can be converted as shown into 3-substituted propenal derivatives 689 (Scheme 128). 359 Scheme 128 3. 1,3-Bis(trimethylsilyl)propene (Me3Si−C−CdC−SiMe3) 1,3-Bis(trimethylsilyl)propene 690 gives anion 691 which is attacked by carbonyl compounds producing 693 and 694 but with low yields and variable stereoselectivity. 360,361 This can be improved by addition of MgBr2, trimethyl borate, or Cp2TiCl (Scheme 129). 362 The reaction proceeds via a six-membered transition state exhibiting a chair conformation 692 (analogous to 447, Scheme 79, section II.G.1). Scheme 129 The reaction of 1,3,5-tris(trimethylsilyl)pentadiene anion 695 with trimethylchlorosilane leads to 1,1,3,5tetrakis(trimethylsilyl)-1,3-pentadiene 696 with 99% regioselectivity in THF while in hexane a mixture of 696 (55%) and 1,3,3,5-tetrakis(trimethylsilyl)-1,4pentadiene 697 (45%) is observed (Scheme 130). 264 Scheme 130 4. 3-(Methylthio)-2-propenyl p-Tolyl Sulfones (MeS−CdC−C−SO2R) 701 3-(Methylthio)-2-propenyl p-tolyl sulfone 698 can undergo either mono- (cf. 699) or double alkylation
Page 1 and 2: Regioselectivity of the Reactions o
Page 3 and 4: Alan Katritzky is Kenan Professor a
Page 5 and 6: Scheme 3 Scheme 4 of γ-attack 11 a
Page 7 and 8: Scheme 10 Scheme 11 predominantly a
Page 9 and 10: Scheme 16 Scheme 17 106) (Scheme 16
Page 11 and 12: Scheme 25 Scheme 26 γ-attack in th
Page 13 and 14: Scheme 35 Scheme 36 Treatment of mo
Page 15 and 16: Scheme 42 Scheme 43 Scheme 44 D. Se
Page 17 and 18: 3. Allylphosphoramides (CdC−C−N
Page 19 and 20: Scheme 58 steric bulk of the carbon
Page 21 and 22: Scheme 65 Scheme 66 lent stereosele
Page 23 and 24: Scheme 72 Scheme 73 te ester can be
Page 25 and 26: Scheme 79 Scheme 80 b. Aminosilyl-S
Page 27 and 28: Protonation with tert-butyl alcohol
Page 29 and 30: Scheme 93 Scheme 94 hydes (Scheme 9
Page 31 and 32: Scheme 100 In reactions of the ally
Page 33 and 34: Scheme 110 Scheme 111 uents in the
Page 35: The γ-alkyl-substituted allylic an
Page 39 and 40: Scheme 135 2. γ-Alkoxyallyl Sulfon
Page 41 and 42: Scheme 146 765 762 768 769 (Scheme
Page 43 and 44: VI. Allyl Anions Stabilized by Thre
Page 45 and 46: Scheme 162. Allyl Anions Stabilized
Page 47 and 48: Scheme 169 Scheme 170 enantiomeric
Page 49 and 50: transition structures 876 of the C(
Page 51 and 52: and ketones if the reaction is carr
Page 53 and 54: silane anions 486 is increased with
Page 55 and 56: (67) Hoppe, D.; Lichtenberg, F. Ang
Page 57 and 58: (287) Gil, J. F.; Ramon, D. J.; Yus

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