9/24 Flashcards
Reactions of ethers and epoxides
what is the first step in the ether cleavage with HBr
the oxygen is protonated to form a good leaving group
when reacting diethyl ether in excess HBr what reaction occurs and what are the products
you will get two products of bromo ethane through an ether cleavage
what are epoxides? why do we like them
they are good reactive intermediates because they contain an oxygen and are a three membered ring with ring strain
what is meta chloroperoxybenzoic acid used for
it is a peroxyacid used to make epoxides from alkenes
what is a peroxide characterized by
a oxygen oxygen single bond
when reacting a cis alkene with m-CPBA what do we get
a cis epoxide, retention of stereochemistry occurs
what type of reaction is the formation of an epoxide with mCPBA in regards to stereospecificity
it retains stereochemistry through a syn addition
why are epoxides useful
they are highly reactive due to ring strain, have oxygen, and create chiral carbons
what are the steps for the acid catalyzed ring opening of an epoxide
the epoxide deprotonates the acid to form a good leaving group
the acid acts as a nucleophile and preforms a backside attack on the MOSt substituted side of the alkene
the epoxide breaks open with the oxygen retaining its stereochemistry and the other carbon inverting its stereochemistry
why does the nucleophile attack the most substituted side of an alkene for an acid catalyzed ring opening of an epoxide
it has the most carbocation like character
how should you make a trans diol?
use an epoxide in an acid catalyzed ring opening with H30+ to form a trans diol
how should you make a cis diol?
use OsO4
what reagents could you use for a base ring opening of an epoxide
NaOme, NaOet, NaOtBu
these are alkoxide ions
where does the base undergo nucleophilic substitution in a base catalyzed ring opening of an epoxide
it attacks at the least substituted carbon due to steric effects
what are the steps to a base catalyzed ring opening of an epoxide
the base (alkoxide ion) will perform nucleophilic substitution on the least substituted side of the alkene and the epoxide will break open
when the epoxide breaks open, the negatively charged oxygen will be protonated by the alcohol solvent (ex. meOH)
