Chem 334 1st Edition Lecture 11Outline of Last Lecture I. Synthesis of aldehydes and ketonesOutline of Current Lecture II. Hydride as a NucleophileIII. Cyanide AdditionIV. Wittig AdditionV. Oxygen NucleophilesCurrent LectureHydride as a nucleophile:O LiAlH4 OHO NaBH4 OHCyanide addition:O N≡ - Na+ OH H3O N O- H-O+-H N HWittig reactions:Witting reactions make alkenes from aldehydes and ketones with aylide addition. Phosphoniumylide(Ph3P+-CH2-) adds carbons and converts C=O bonds to C=C bonds. Ylides can be formedfrom an SN2 reaction. They act as a good nucleophile and will react with primary and secondary alkyl halides:Ph3P: CH3 – I SN2 Ph3P+-CH3The negative charge on the carbon is what causes Ph3P+-CH2- to act as a good nucleophile. This required agood base to pull a hydrogen off of CH3. Some possible bases that can do this are nBuLi, NaH, and NaNH2.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. The formation of this product is the driving force of the reactionO O- O PPh3Ph3P+-CH2- Ph3P+-CH2- O PPh3 Ph3P Br nBuLi Ph3P+ - OFor this reaction, whatever is directly attached to the phosphorus will replace the oxygen in the final product. When using non-symmetrical Ph3P in Wittig reactions, you will get a mixture of X and E diosteriomers. We can use a modification of the Witting reaction, called the Horner Wadsworth EmmunsReaction, to get the more stable alkene, which will be the E alkene. The difference is in the nucleophile. O OOPhPh P EtNaHPh P Et H PhPh H Et - EtIn the reaction above, the phosphate ester is an electron withdrawing group, which allows resonance. Resonance slows down the reaction and allows the more stable product (E) to form.Oxygen Nucleophiles:There are several variations of oxygen nucleophiles;A. H2O gem diols:For this reaction, the carbon-oxygen double bond in the starting material becomes two separate OH groups. Overall, this reaction is not a very useful one.O H2O/H+or OH- OHH H OHB. Alcohols Hemiacetal:For this reaction, the carbon-oxygen double bond is replaced by an OH and an OR group bonded to the same carbonO H+ or OH- OH H HOR H ORMechanism: Base CatalyzedO O- OH H O- R R H OR H – OR R H ORMechanism: Acid CatalyzedO O+ O–H OH H H–O+–R R H H–O–R R H O+–R R H OR H H H–O–R Most sugars, like glucose, are hemiacetials. Hemiacetals are generally unstable unless they are formed into a 5 or 6 membered ring.OH H H+ or OH- O O OH C. Alcohols acetals:These reactions essentially take hemiacetals and react them further. However, these reactions can only take place under acidic conditions. Acetals are used as protecting groups for aldehydes and ketones, as they are unreactive to basic conditions, reducing agents, organometallics, H2, and oxidation.O HOR OH H+/HOR OR OR ORMechanism:OH H–O+–R +O O+–R O+–R OROR H OR R–O–H OR H–O–R ORNotice that these reactions can go in either direction (forwards or backwards). These reactions are driven to completion based on the amount of water in the reaction. We remove H2O to get a product and add H2O to get the starting
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