CHE 331-80011.17 - L6.l/v m C H ‘ I 1 7#1“ o...

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Unformatted text preview: L6,.l?{/v m. C: H ‘ I" / 1/ 7 / #1“ 11/11/13 o Stereospecific Reactions I) A reaction is stereospecitic if a particular stereoisomeric form of the starting material reacts in such a way that it gives a specific stereoisomeric form of the product. -) Example: cis- and trans-2-butene give stereoiSOmeric products. Rene/inn l mfi ‘H‘ 1le C H lirK—IH 1| m1, C ((‘|\ H/ \Clh n _n u r’ ‘11 C1 | ‘ (rans- 2- Bulch (2 R35 l-2,3»l)i hrmnnbu lane (a Int'SO compound) Reaction 2 l C”: :H: ; H‘C\ /n i;r\:,H H\:’Br (‘ Br. (. l H I ‘ l /C\ ‘ «(S I ‘\ 113C H H Br Br = H (11‘ CH: cix-l-Bulcne (ZRJR) (25,35) —f'\ ml" Mechanistic explanation: Chapter 8 24 12 lllllll T r Q23 Wymr % @4277?ch _; MS wag; figs/65 & mesa L 11/11/13 O Halohydrin Formation I} If halogenation is carried out in aqueous solvent, the water molecule can act as a nucleophile to open the halonium ion. * The product is a halohydrin. \ / , I | | | C=C + x, + ll,0-———> ~—~C-C—- + —-—C—-—C—- + HX / \ * ‘ | l l ! UH X X . . , , ' ir.‘ X = Cl or Br Halohydrin vic-Dihalide D (major) (minor) a" Mechanismb if 1‘1 f9/“ 07" A 2~.U a7 6 r1 H . fl. 14H @r ~—~> 20 "‘ 19 1* ,HH 6 r 6f "7 Ch 8 H 25 H apter H or If @r at l—e/gds +0 mm but mag Cm” 10% ‘, " ., ‘ 1] «I lay) \ I vaCLLLU a; LLLI _ Dam Waflg I) In unsymmetrical alkenes, the bromonium ion will have some of its 5+ charge density on the more substituted of the two carbons. It The water nucleophile will tend to react at the carbon with the most 5+ charge. H .... H“ r~ CH, \05 \ ()H HXL\ “‘1: m I /;"_'"‘:le. I V :6H. C=CH. : CH. CH1 " CH; C CH?!” ’ ) CH; C CHzlh‘ + H;(.)‘ ./ x / | l H‘ Br CH‘ CH1 (73%) 13 ./ 0H005 o ' a ‘ > ‘ 1 ‘80 w (“Kai I) Carbenes add to double Eggs in a stereospecific manner l6 R“ H H Ru, (V 1“ R The additionnftt'XJs “(at “ V. M]: .. \C. .............. .. L" nereogpecllic. mmng'mum H V \ R \‘K / of flu- nlkcnr Inn 1 v Ci ‘ H S \(. (mg-1:3:llg‘npz‘ggn-illitinlly H [I] ( “(‘1 H lhopnuluct.) 4 m I} Dihalocarbenes are romIéZWZ elimination of compounds such M . ,4 C as chloroform L, .. .. .. 1 R—Q:-K+ + H «11:15: 12—94; + «:03 + K+ W =(ICIZ + :91: ‘5‘ N H Dichlorocarbene ’ /', , / C Q 1 A C '— / WWW. . , \ . l {v.2 \ K’Oi‘7HTaC‘C'“)V-'O"H+'C, U C; " ‘ ‘ ‘ i \ W Li / C I C \ \ \ ‘ I / 11/11/13 ix} 1: P C(LN bQ wk. 0 v 2} M K 4‘ WV 5" um 1:4: r it}: 11";19'17'14'111 1‘, 11,1 ‘1 HLW‘Kr'. O Divalent Carbon Compounds: Carbenes I} Carbenes have divalent but neutral carbons with a lone pair of electrons. 0 Structure and Reaction of Methylene ‘ + _ . heat . _ __ _ :CHg—EyzN. ———')0r1igh‘ -CH2 + -N=N. . - , ,N ; L Diazomethane (Cm2$§e N‘tmberig ON 10% %(D Up I) Methylene reacts with alkenes to form W. \C ml] \C C/ = : V 9 ————> - / \Q/ ~ / \/ \ C / \ H H Alkene Methylene Cyclopropane ChapterS 27 oQHLNz ‘2 Elam rywvmm ~ 7 ~ 1 ‘13 «0mg; \efllmose hill?) at ogcgd lean/1m: Cirbwg wmomflh 0 Reactions of Other Carbenes: Dihalocarbenes Chapter 8 e9 shag bci’be % m c C15 fives C531 Vac/1f) gives trams « EMMA?! to 06% {CA—e Axooifl wad Wm 11 C} l€W$ 14 Carbenoids: The Simmons-Smith Cyclopropane Synthesis A carbene-like species is formed which then reacts with alkenes to form a cyclopropane. ~k CHle ‘1‘ Zn(Cu) "——) A carbenoid O C‘l’f) C1330 Call/98,1132. 9: Q CHZIZ/Zn(Cu) ether Chapter 8 ' SCip€f 1’0 036 O Oxidations of Alkenes: Syn 1,2-Dihydroxylation I) Either 0504 or cold KMnO. will give cis-1,2 diols (glycols). (I ) (,)s( )4. pyridine — a * CH ‘ — ,H, CH1CH CH“ (2) MIBSOJ/HIO or NaHSOJ/HZO 3%” CI‘ - ()H OH 1,2-Pr0panedi0l (propylene glycol) Propene o Mechanism for Syn (Cis) Hydroxylation of Alkenes: + MnO /‘ \ \\ CUM \ Im + Mn()4 —> —,> H H Ull pink ()\ /0 on ()H brown ppt. u “\ ris-l,l-Cpclnpcnmncdinl O O ‘ m mesn compuundl Chapter 8 » mean we (“6,01 chem o NJlflOAr 1‘.) (Lee? M130"; ’@ "1—4 ) wwm CU a “z c mm:-5Vu 11/11/13 H on fire-6t) 15 11/11/13 O OH 0 0H 0 ML co“ /E\/lk Ph OMe + KMn04 W Ph : OMc + Ph OMe OH OH 50% 50% Taxol Synthesis Mulliple sleps 0 ()H 0 0 /\/U\ gosogomg. (0.2%). NMO —-—» JL Ph \ OMe_‘—’Ph' OMe -—’ Ph’ \NH O chiral amine ligand (0.5%) R, ————-> («me hckiw) HO Ph ()1 l 99% cc ' (72 92 yield) OH Puclimxel side chain OCOCHJ O Oxidative Cleavage of Alkenes ID Reaction of an alkene with hot KMnO,l results in cleavage of the double bond and formation of highly oxidized carbons. w" /0 /0 CH§CH=Z=CHCH‘ "M"0"0” "'9 2 CH‘C 39—» 2 Cth * . ‘ heal ‘ \ ‘ \ O OH (cis or trans) Acetate ion Acetic acid (Tm r1. KMn04,OH EH3 CHWCH C=§=(.TH~ —'“:i‘i.————+ CH CH,C=O + o=c=o + H o - 1 . ~ (2) HQ 3 - 2 Chapter 8 ‘0 00+ Cioubm 13000 3“ Mug; 0 Wm Mm Whomle a (L ”" 3M3 16 moo W5 -‘L> dioxide m L {Rimes WWW 0 Solved Problem I) An unknown alkene with formula €7sz yields only the following product on oxidation with hot KMnO. (I) KMIIOJ. H30. (i ? C H CH CCH CH CH CH C—OH 7 l2 (2)1410? 3 2 ’ 2 2 2 “ What is the structure of the alkene? I? Answer: Since no carbons are missing in the product, the alkene must be part of a rigg in the original molecule. CH; (1) KMnOJ. H:(), f (")1 t (H) E} CHfigngH,CH~CH1C—OH (2) H,O - ~ ~ - -4~_ Unknown alkene \(QCK ‘iC‘1 (l-methylcyclohexene) RC) C e ()6; Chapter8 33 o Ozonolysis of Alkenes It Cleavage of alkenes with ozone leads to less highly oxidized carbons than products from cleavage with hot KMnO4. CH, CH3 (i I (ll 0 CH Cl '-78”(‘ l . ‘= . ‘ ,I~ ' 3 p r ‘ y: ‘ V ‘ (,Hsc L.ll( H] —————~———>(2) WHOM CHJL 0 + (.ll‘(,,ll Z-Methyl-Z-butene Acetone Acetaldehyde (liH‘ (liHA (H) , (Ii OUCHVCL. ~78 C I (.IIJLH CH (.112 —-—————-—>(1’ Zn/HOAC ( ILL" (11 + II( 11 S-Methyl-l-bulene Isobutyrnldehyde Formaldehyde Chapter 8 11/11/13 17 9?de 33 ...
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