Objective 14. Develop synthesis strategies for organic synthesis. Skills: Draw structure ID structural features and reactive sites (alpha C, beta C, LG, etc.) ID Nu - and E + use curved arrows to show bonds breaking and forming show delocalized electrons with resonance structures. Key ideas: Starting material --> target compound. Count # of C s bigger or smaller compound. ID functional groups in starting material and target compound. What part(s) of the starting material and target compound are the same? ID bonds that break/form. Brainstorm possible reactions.
Reaction Roadmap: Which groups has an α-c? (2 types of α-c) What are β-keto acids/esters used for? What group makes α,β-unsaturated carbonyls? alkyne alkane alkene alkyl halide amide acid ester alcohol R-M aldehyde ketone nitriles Diols, cyanohydrins, imines epoxide Ether acetal w/ ROH
The Journey!
ORGANIC SYNTHESIS STRATEGIES Convert one functional group to another Move a Functional Group from 1 C to adjacent C Make a C-C bond to make a bigger molecule How? See Structural Features è Tells you Reaction Type
Structural Features tell us: Which atom or bond reacts Reaction Type How to make a Compound C=C pi bond (including conjugated diene and aromatic) C-O, C-X, C-N compounds: carbon, leaving group (HOH, ROH, NH 3, X - ), H bonded to carbon, epoxide C=O compounds: carbonyl carbon, carbonyl oxygen, carbon (C next to carbonyl C), carbon TWO structural features: -hydroxy aldehyde/ketone (see enolates), -unsaturated aldehyde/ketone (see enolates) -keto ester (see ester enolates)
Reaction Type Acid-Base Nucleophilic Substitution Nucleophilic Acyl Substitution EAS Elimination Electrophilic Addition Nucleophilic Addition Structural Features Acid H (see pk table) Base (see pk table) carbon, LG Reacts with Nu: - carbon, H bonded to carbon, LG Reacts with Nu: - C=C pi bond Reacts with E +
Fill in the Table. Classify carbon, H bonded to or carbon, enolate. What is used to make a C-C bond? Atom Type Nucleophiles Electrophiles hydrogen carbon nitrogen oxygen X Bond
Many Organic Reactions are Reversible Example: OR How does ethanol react? How can you make ethanol? Ethanol Structural Features: carbon and LG ==> Substitution H bonded to carbon and LG ==> Elimination Basic O and Acidic H ==> Acid-Base C-O bond ==> Oxidation Several Ways Ethanol Reacts è Several Ways to Make Ethanol
The following reaction has been reported in the chemical literature. Write the structure of the product(s). Structural Features: Carbonyl C Carbonyl C base H on carbon no H on carbon H on carbon H on carbon
Identify the reagents appropriate for each step in the following synthesis: Structural Features: Carbonyl C Carbonyl C C=C H on C Br on C, unsat d H on C H on C H on C
Aldehydes/Ketones and Acids Can be Halogenated at the α-c via an Enol Mechanism involves an enol. Compare the reaction of an enol with X 2 to an alkene with X 2. Does NOT work with acids, esters, or amides (not converted to enols) under these conditions. Different conditions (Hell-Volhard-Zelinsky)
Outline a reasonable mechanism for the following reaction: Structural Features: Carbonyl C What else? Carbonyl C What else?
Suggest reagents appropriate for each step in the synthesis. Structural Features: Carbonyl C Carbonyl C What else? Br on which C?
ORGANIC SYNTHESIS STRATEGIES How? See Structural Features è Tells you Reaction Type Convert One Functional Group To Another Structural Features: carbon and LG ==> Substitution Structural Features: C-O bond to C-O, C=O ==> Oxidation
ORGANIC SYNTHESIS STRATEGIES How? See Structural Features è Tells you Reaction Type Move a Functional Group from 1 C to adjacent C Structural Features: C and LG è Sub H on C and LG è Elim LG on different C H on C
ORGANIC SYNTHESIS STRATEGIES How? See Structural Features è Tells you Reaction Type Make a C-C bond to make a bigger molecule Use a carbon nucleophile and a carbon electrophile ID structural features: addition ID structural features: substitution Which C is electrophilic? Which carbon nucleophile to use? RMgX, CN -, acetylide ion, enolate or ester enolate
C&EN, 6/2/14, p. 24 (http://cen.acs.org/articles/92/i23/cleaning-conundrum.html ) Eastman Chemical Invents a New Cleaning Solvent for household and industrial cleaning products that meets the EPA standards for toxicity and VOC content. Trade Name: Omnia Propose an efficient synthesis of Omnia from. Replaces: ethylene glycol monobutyl ether (CA hazardous substance) dipropylene glycol monomethyl ether (VOC)
Propose an efficient synthesis of Omnia from. Trade Name: Omnia Structural Features: carbonyl C and carbonyl O (ester) H on C OH on C ( -hydroxy ester, not a -keto ester) O-H group: O is basic, H is acidic
http://cen.acs.org/articles/91/i12/limits-lithium.html 3/25/13, CEN, p. 15 Limits Of Lithium It helps millions with bipolar disorder, but toxicity problems and side effects have scientists looking for alternatives by analyzing the drug s mysterious mechanism. Subanesthetic infusion of Ketamine (anesthetic agent) can relieve the symptoms of depression and suicidal urges in a matter of hours. The effect lasts about a week, whereas commonly prescribed antidepressants usually take weeks to work. (C&EN, Aug. 23, 2010, page 8). Design a synthesis of ketamine from: Ketamine Structural Features: How to connect the 2 molecules? Structural Features:
Note: Aldol and Claisen reactions form a C-C bond What else can an enolate or ester enolate ion react with? +?? --------> +?? -------->
Use Enolate in Nu: - substitution reaction Problems with this method: 1. Elimination competes with substitution 2. Poor yield Is there a Better way? (Klein, Organic Chemistry, p. 1063)
Objective: use malonic ester synthesis and acetoacetic ester synthesis to make a C-C bond α to carbonyl C Malonic ester synthesis: Lengthen chain by 2 carbons Use diethyl malonate Remove α-h to form enolate Enolate = Nu: - Acetoacetic ester synthesis: Lengthen chain by 3 carbons Use ethyl acetoacetate Remove α-h to form enolate
Alkylate the α carbon in an aldehyde/ketone: Use Acetoacetic Ester. Alkylate α carbon in an organic acid: Use Malonic Ester. Decarboxylation Reactions Are Important in Biology
http://cen.acs.org/articles/92/i26/new-way-stick.html Sirrus Company makes 1,1-disubstituted alkene monomers for use in adhesives, sealants, coatings, and inks. What type of reaction occurs?
Other ORGANIC SYNTHESIS STRATEGIES Shorten (Break C-C bond) a carbon chain: 1. ozonolysis 2. Decarboxylation Reaction Dicarboxylic acid (with 1 C between -COOH) -- heat --> acid + CO 2 E.g., Malonic acid (propanedioic acid) decarboxylation: Which bond breaks?
Other ORGANIC SYNTHESIS STRATEGIES Shorten (Break C-C bond) a carbon chain: 2. Break a C-C bond by decarboxylation of a. dicarboxylic acid b. β-keto acid -- heat --> CO 2 + enol ----> ketone 1 C from -COOH is α-c Draw structure of product 2 C from -COOH is β-c
Other ORGANIC SYNTHESIS STRATEGIES Shorten (Break C-C bond) a carbon chain: 3. Biology: Glucose (C 6 ) undergoes glycolysis to form pyruvate (C 3 ). (reverse aldol condensation) Which bond breaks?
Identify Compounds A, B, and C in the following synthetic sequence. NaOCH 2 CH 3 Compound A (C 6 H 10 O 2 ) ------------------> + H 2 C(CO 2 CH 2 CH 3 ) 2 ethanol Compound B (C 13 H 22 O 6 ) heat CH 3 CH(CH 2 CO 2 H) 2 <-------------- Compound C (C 7 H 10 O 6 ) H 2 C(CO 2 CH 2 CH 3 ) 2 = malonic ester
Objective: describe the mechanism of this reaction Compare C-C bond making methods: 1. Grignard (to make ROH) 2. Acetylide ion (alkyne ---> other functional groups) 3. CN substitution (to make nitrile ---> convert to acid) 4. Enolate ion (Aldol, Claisen, RX, malonic ester, acetoacetic ester)
Conjugated dienes undergo 1,2 and 1,4 addition (Klein, Ch. 17) α,β-unsaturated ketones undergo 1,2 and 1,4 addition (Michael Reaction) How do you make an α,β -unsaturated ketone?
Common Michael Donors and Acceptors (see Klein, Table 22.2, p. 1067) Michael Donors Michael Acceptors R 2 CuLi (RMgX too strong)
CEN, 4/2/12, p. 8 New Class of Superbases Cyclopropenimine is a very strong base (3.5 orders of magnitude higher than that of comparable guanidines) and catalyzes reactions up to 800 times faster. a. Explain why Cyclopropenimine is a strong base. (Hint: draw the structure of the conjugate acid of Cyclopropenimine.) b. With which reactant does this base react? c. Draw the structure of the product. (Hint: Michael addition)
CEN, 4/2/12, p. 8 New Class of Superbases Cyclopropenimine is a very strong base (3.5 orders of magnitude higher than that of comparable guanidines) and catalyzes reactions up to 800 times faster.
It is pretty easy to form a C-C bond at an - C. But it is NOT easy to form a C-C bond at the - C. -substituted carbonyls are common in insecticides and drug candidates. A new -arylation makes an intermediate used to synthesize serotonin reuptake inhibitors. (http://cen.acs.org/articles/91/i48/metal-duo-makesaryl-ketones.html)
http://cen.acs.org/articles/91/i11/synthetic-shortcut-erythromycin-precursor.html 3/18/13, CEN, p. 11 Synthetic Shortcut To Erythromycin Precursor Where does the carbonyl C come from? 1978: 33 steps 1979: 39 steps 2009: 23 steps 2013: 14 steps
http://cen.acs.org/articles/92/i4/year-new-drugs.html
http://cen.acs.org/articles/88/i39/genotoxic-impurities.html Making Drugs: Multistep synthesis often involves undesirable materials, e.g., genotoxic impurities that damage DNA and may cause cancer.
http://cen.acs.org/articles/88/i39/genotoxic-impurities.html CEN, 9/27/10, Genotoxic Impurities
http://cen.acs.org/articles/88/i39/genotoxic-impurities.html CEN, 9/27/10, Genotoxic Impurities
http://cen.acs.org/articles/91/i19/clicking-pyrroles-place.html 5/13/13 Clicking Pyrroles Into Place Map the atoms in reactants and products.