Ethers and Epoxides Flashcards
what reaction converts ROH into ethers
Williamson ether synthesis
what are the two types of williamson ether synthesis
intermolecular, and intramolecular
what reagents are needed for Williamson ether synthesis
strong base, and an electrophile
what are examples of strong bases used for Williamson ether synthesis
LDA, BuLi
what is the product of intermolecular Williamson ether synthesis
ether
what is the product of intramolecular Williamson ether synthesis
cyclic ether
what is the mechanism for williamson ether synthesis
Sn2
characteristics of intermolecular Williamson ether synthesis
between molecules, slow
characteristics of intramolecular Williamson ether synthesis
within a molecule, fast
why are ethers great solvents
they react with very few reagents
characteristics of ethers
- stable in basic conditions
- resistant to nucleophilic attack
what is the mechanism for acidic cleavage of ethers
- proton transfer
- Sn2
what dictates the reactivity of hydrogen halides toward the cleavage of ethers
their general acidity and nucleophilicity
HI > HBr»_space; HCl
what kinds of ethers undergo acid cleavage via Sn1 and what do they form
tertiary, allylic, and benzylic ethers (study what these are); form stable carbocation intermediates
what is the reagent for acidic cleavage of ethers
binary acid
what is the product of acidic cleavage of ethers
alcohol
what is the mechanism of acid cleavage via Sn1 to form stable carbocation intermediates
- proton transfer (forms oxonium)
- leaving group leaves (forms benzylic or vinylic carbocation)
what is the relative acidity between hydroxyl protons and terminal alkynes
hydroxyl protons > terminal alkynes
protecting groups characteristics
- easily added to the sensitive functional group
- resistant to the reagents used to transform the unprotected functional group or groups
- easily removed to regenerate the original functional group
what are the steps of the protection of -OH groups
- protect
- react
- deprotect
what reagent is used to protect -OH
TMSCl or ROTMS
what is the reactant for protection of -OH
1,2-difunctionalized group with a functional group that should react instead of the alcohol group
what are the good protecting groups
TMSCl (trimethylsilyl chloride), and ROTMS (a silyl ether)
what reagent can be used to deprotect
Bu_4N^+F^-
what is an epoxide
cyclic ether
what is the most acidic proton site on an epoxide
the alcohol
is alkoxide a good nucleophile or electrophile
nucleophile
which Sn2 attack is faster: intramolecular or intermolecular?
intramolecular
what are the steps of intramolecular Williamson synthesis of epoxides
- proton transfer
- cyclization via Sn2
what is the purpose of Williamson synthesis of epoxides
turning an alkane alcohol into an epoxide
what is the purpose of synthesis of epoxide with peroxycarboxylic acids
create an epoxide from an alkene
what reagent is required to synthesize an epoxide from an alkenee
mCPBA with an aprotic solvent (usually CH2Cl2)
what are the two precursors to an epoxide
- halohydrin
- epoxidation of alkene
how does stereochem affect epoxidation of an alkene
cis alkene –> cis epoxide, trans alkene –> trans epoxide
what reagents do you need for the two steps of a ring-opening reaction of epoxides
- alkaline
- protic
what is the precursor to a 1,2-difunctionalized compound
epoxide
what is the mechanism for the alkaline nucleophilic ring-opening of epoxides
Sn2, then proton transfer
what do you do if there is an alkoxide with an sp3 C
take a traditional proton transfer
what intermediate forms when the ring-opening step occurs in alkaline conditions
alkoxide
which carbon does the nucleophile attack in an acid-catalyzed ring-opening
more substituted carbon
what are commonly used H-Nu for synthesizing 1,2-difunctionalized alcohols
H3O+, ROH; H3O+; HX
why is stereochemistry variable in ring opening of epoxides
- nucleophile backside-attacks the carbon atom (opposite side from LG)
- attached methyl group is repelled away by nucleophile
