Organic Chemistry II: Chapter 13: Ethers and Epoxides; Thiols and Sulfides Useful Reagents

RX

An alkyl halide. Used for the alkylation of alcohols or thiols. First, the alcohol or thiol is deprotonated with a base, such as NaH or NaOH, and the resulting anion is then treated with the alkyl halide, thereby installing an alkyl group

1) Hg(OAc)2, ROH

2) NaBH4

These reagents will achieve alkoxymercuration-demercuration of an alkene. This process adds H and OR in a Markovnikov fashion across the alkene.

HX

Will convert a dialkyl ether into two alkyl halides via cleavage of the C-O bonds. Will also react with an epoxide, thereby opening the ring, and installing a halogen at the more-substituted position.

MCPBA

meta-Chloroperoxybenzoic acid. An oxidizing agent that will convert an alkene into an epoxide.

RCO3H

A peroxy acid. An oxidizing agent that will convert an alkene into an epoxide. MCPBA is an example of a peroxy acid.

1) Br2, H2O

2) NaOH

Alternative reagents for converting an alkene into an epoxide.

(CH3)3COOH, Ti[OCH(CH3)2]4, (+)-DET or (-)-DET

Reagents for enantioselective (Sharpless) epoxidation.

NaOR (or RONa)

An alkoxide ion is both a strong nucleophile and a strong base. It can be used in a Williamson ether synthesis (reacts with an alkyl halide to form an ether), or to open an epoxide under basic conditions (the alkoxide ion attacks the less substituted position).

NaCN

A good nucleophile that will react with an epoxide in a ring-opening reaction.

NaSH

A very strong nucleophile that will react with an epoxide in a ring-opening reaction. NaSH can also be used to prepare thiols from alkyl halides.

RMgBr

A Grignard reagent. A strong base and a strong nucleophile. Will react with an epoxide in a ring-opening reaction, to attack the less-substituted side (it is not possible to use acidic conditions and have the Grignard reagent attack the more-substituted side - see the previous section on common mistakes to avoid).

LiAlH4

Lithium aluminum hydride is a source of nucleophilic hydride. It will react with an epoxide in a ring-opening reaction, to attack the less-substituted side (it is not possible to use acidic conditions and have a hydride ion attack the more-substituted side - see the previous section on common mistakes to avoid).

[H+], H2O (or H3O+)

Aqueous acidic conditions. Under these conditions, an epoxide is opened to give a trans diol.

[H+], ROH

Under these conditions, an epoxide is opened, with a molecule of the alcohol attacking a protonated epoxide at the more-substituted position.

NaOH/H2O, Br2

Reagents for converting thiols into disulfides.

HCl, Zn

Reagents for converting disulfides into thiols.

H2O2

Strong oxidizing agent, used to oxidize sulfides to sulfoxides, and then further to sulfones.

NaIO4

Oxidizing agent, used to oxidize sulfides to sulfoxides.