Advances in the stereoselective synthesis of antifungal agents and ...

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Chapter 2 43This approach clearly explains the formation of the S-isomer from the(-) - DIP chloride 21a and the R-isomer from the (+) - DIP chloride 21aunless the steric bulk of the carbonyl moiety is changed, as in the case of t-butyl phenyl ketone or in the case of acyl silanes.A different mechanism has been proposed for Corey'soxazaborolidines 11 21c. It constitutes an alternate chair transition stateassembly to explain the origin of the observed enantioselectivity inoxazaborolidine catalyzed reductions of prochiral ketones.According to this model ( Scheme 2.7 ), the 1,3 diaxial interactionbetween the R L and R S substituents of the ketones and the oxazaborolidonemethyl group differentiates between the two diasteroisomeric transitionstates 22a and 22b, leading to the major R-product and the S-enantiomersas minor products 12 .Corey's oxazaborolidines can be used in catalytic amounts (5% molarwith respect to the ketone); the source of hydride is BMS or BH3 -THF inan equimolar ratio with the ketone. A complete investigation of the reactionconditions has been reported by the Merck Sharp and Dohme departmentof process research 12 .RsR LOMeHHBBHNOPhPhH21cHydride transferR LRsMeHOHBBHNOPhPhHRsR LMeHOHBBHNOPhHPh22aFavoredRepulsionDisfavoredScheme 2.7: Mechanism and transition state for the chiral reduction of ketones withOxazaborolidine 21c.22b
Chapter 2 44Chiral phosphine complexes of late transition metals in a low oxidationstate catalyze enantioselective reductions in a homogeneous phase. Noyorideveloped an interesting approach for the enantioselective reduction ofprochiral α-substituted ketones employing an enantiopure Ru (II) complexwith 2,2'-Bis-(diaryl phosphino) 1,1'Binaphtyl (BINAP) 21e/d.These organometallic catalysts are endowed with functionality andaxial chirality and allow a differentiation between diasteroisomeric transitionstates differing in energy of only 10 KJ/mol. Such molecular catalysts arenot only able to accelerate the reaction rate, but also to control thestereochemical outcome of the reaction in an absolute sense.BINAP 21e, a fully arylated, C2 symmetrical chiral diphosphine, is oneof the most effective chiral ligands that have been designed 13 (Fig. 2.4).BINAP ligands can accommodate a wide variety of transition metals toform conformationally unambiguos seven membered chelate ringscontaining only sp 2 carbons.PAr 2PAr 2PAr 2PAr 2(R)-BINAP(S)-BINAPFigure 2.4: R- and S-BINAP 21e.The single crystal X-Ray analysis of certain square planar oroctahedral BINAP complexes indicates that the seven membered rings havea higly skewed configuration that provides a distinct chiral microenviromentin which the phosphophenyl groups are oriented into axial and equatorialdirections 14 ( Fig. 2.5 ).
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Advances in the stereoselectivesynt
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ACKNOWLEDGMENT:I would like to than
Page 6 and 7:
Summary:Numerous drugs are chiral,
Page 8 and 9: IndexII2.2 Synthesis of enantiopure
Page 10 and 11: IndexIV4.4. Stereochemical Assignme
Page 12 and 13: IndexVImethyl amine 69 1446.6. Stud
Page 14 and 15: IndexVIII8.23.3.1 Desilylation usin
Page 16 and 17: Chapter 1 11.Introduction1.1. Chira
Page 18 and 19: Chapter 1 3The concept of stereoche
Page 20 and 21: Chapter 1 5switches is in the area
Page 22 and 23: Chapter 1 7-bonds 9 . It is now wid
Page 24 and 25: Chapter 1 914CH 3Cyt P-450 DMOH3O 2
Page 26 and 27: Chapter 1 11piperazine) is also the
Page 28 and 29: Chapter 1 13The four stereoisomers
Page 30 and 31: Chapter 1 15single enantiomers and
Page 32 and 33: Chapter 1 17was synthesized by the
Page 34 and 35: Chapter 1 19HOHODesmolaseHOCholeste
Page 36 and 37: Chapter 1 21formic acid results in
Page 38 and 39: Chapter 1 23inactivation. 113 . Bec
Page 40 and 41: Chapter 1 25Two newer compounds whi
Page 42 and 43: Chapter 1 2715 is an advanced repre
Page 44 and 45: Chapter 1 29transformation of the a
Page 46 and 47: Chapter 1 31Enantioselective synthe
Page 48 and 49: Chapter 1 33+R,S DRUG ANCHOR R MOLE
Page 50 and 51: Chapter 1 35solubilized in hot etha
Page 52 and 53: Chapter 2 37RsORmRmRsRLRL RRRLH - A
Page 54 and 55: Chapter 2 39The stereochemistry and
Page 56 and 57: Chapter 2 41An asymmetric reducing
Page 60 and 61: Chapter 2 45PhaxeqP 1MP 2axeqPhP 2M
Page 62 and 63: Chapter 2 47pyrrolidine ] 20 , LAH-
Page 64 and 65: Chapter 2 49Enzymatic reactions are
Page 66 and 67: Chapter 2 51As [ES] in equation 4 c
Page 68 and 69: Chapter 2 53E+AK 1AK -1AEAK 2AE+PE+
Page 70 and 71: Chapter 2 552.2.4 Lipases.Most lipa
Page 72 and 73: Chapter 2 57enzyme intermediate can
Page 74 and 75: Chapter 2 59projecting above the pl
Page 76 and 77: Chapter 2 612.3.1.1. Step 1: Adduct
Page 78 and 79: Chapter 2 63A -+ ROHRO - + AH'RO 2
Page 80 and 81: Chapter 2 65There are various effec
Page 82 and 83: Chapter 2 67The reactions were foun
Page 84 and 85: Chapter 2 69Yamanaka and coworkers
Page 86 and 87: Chapter 2 71sodium or potassium car
Page 88 and 89: Chapter 3 73The reaction is quite s
Page 90 and 91: Chapter 3 75literature as the best
Page 92 and 93: Chapter 3 77dry solvents and, is ch
Page 94 and 95: Chapter 3 79XXOH+ H 2 NDry K 2 CO 3
Page 96 and 97: Chapter 3 81substituents are the mo
Page 98 and 99: Chapter 3 83induces a rotation of t
Page 100 and 101: Chapter 3 85very sharp and it was p
Page 102 and 103: Chapter 3 87Raney NickelOH Br MeOH;
Page 104 and 105: Chapter 4 8933a-m were hydrolysed t
Page 106 and 107: Chapter 4 91benzo[b]furane (entries
Page 108 and 109:
Chapter 4 93hydroxy or amine groups
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Chapter 4 95the products with ethyl
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Chapter 4 97NCO 2 HNCO 2 H(±)34c(-
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Chapter 4 99NNH37CO2EtOH(±)-27a(+)
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Chapter 4 101As already outlined ab
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Chapter 4 103(+)-(S)-2-octylimidazo
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Chapter 4 105CNNH N2 NCN nC 6 H 13N
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Chapter 4 107key step is the conver
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Chapter 4 109reverse addition in th
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Chapter 4 111which was eliminated e
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Chapter 4 113separate (±)-57a and
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Chapter 5 115to avoid this side rea
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Chapter 5 117Complete degradation o
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Chapter 5 119Entry R T °C Product
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Chapter 5 1212:1:3 in weight. All t
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Chapter 5 123reaction conditions we
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Chapter 5 125Entry Substrate R Time
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Chapter 5 127experiments. But it wa
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Chapter 5 129OClOSAM IIPH=7; R.T.OH
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Chapter 5 131OHOXHOHRHK 2 CO 3 ; Me
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Chapter 6 133HCuSO 4 .5H 2 O,NH 4 O
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Chapter 6 1356.2.1 Heteroannullatio
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Chapter 6 137This discovery allowed
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Chapter 6 139OH(±)-62OHFigure 6.1
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Chapter 6 141Entry Substrate R Time
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Chapter 6 143HOH58-a-c,e,h-lRPdCl 2
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Chapter 6 145afforded the benzo[b]f
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Chapter 6 147RR[P(Ph) 3 ]Pd°OHOPh
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Chapter 6 149H2-IodophenolOHOH(±)-
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Chapter 6 151presence of base as de
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Chapter 7 153A chiral lithium alumi
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Chapter 7 155derivatives were tried
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Chapter 7 157Finally an hypothesis
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Chapter 8 159were washed with a sat
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Chapter 8 16145 min, the mixture wa
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Chapter 8 1638.9 Decarboxylation of
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Chapter 8 165Alcohol 27a (0.2 mmol)
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Chapter 8 167for 48 h. After coolin
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Chapter 8 169room temperature for t
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Chapter 8 171in CH 2 Cl 2 and washe
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Chapter 8 1738.26 Screening of lipa
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Chapter 8 175Na 2 SO 4 . After remo
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Chapter 8 177NMR and MS analysis we
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Chapter 8 179Argon was bubbled thru
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Chapter 8 181IR (CHCl 3 ): ν cm-1=
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Chapter 8 183GC-MS: 305 M + (68%),
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Chapter 8 185[α] 20 D -5.7 (c 1.75
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Chapter 8 187Synthetic method 7.7.1
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Chapter 8 189(R,S)-(±)-1-(2-Octyl)
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Chapter 8 191M.P. = oil.Elementary
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Chapter 8 193Synthetic method 7.11.
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Chapter 8 195(±)-N-1-(2-Octyl)-2-t
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Chapter 8 197IR (CHCl 3 ) ν cm-1 =
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Chapter 8 199(±)-1-(4-Fluorophenyl
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Chapter 8 201Physical and spectral
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Chapter 8 203(±)-1-(Phenyl)-2-prop
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Chapter 8 205128.61, 128.87, 130.39
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Chapter 8 207min.Physical and spect
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Chapter 8 20913C J MOD NMR (CDCl 3
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Chapter 8 211(±)-2'-Methylphenyl-2
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Chapter 9 213References chapter 1:1
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Chapter 9 21531) De Felice, R.; Joh
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Chapter 9 21768) Brodie, A.M.H. in
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Chapter 9 219112) Brodie, A. M. H.;
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Chapter 9 2214) Karabatsos, M.C. J.
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Chapter 9 22334c) Blow D. Nature 19
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Chapter 9 22567a) Kundu, N.G.; Pal,
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Chapter 9 22712) Thompson,A.S.; Hum
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