Creating DIOLS from alkenes... quick Q

[anonymuz]

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Anyone know which reagents off the top of their heads or have any source as to which reagents will add diol to alkene in:
1- trans fashion
2- cis

ie) alkene + KMnO4 -> cis diol
ie) alkene + OsO4, something -> cis

 

[ddnguyen6]

form an epoxide by MCPBA with an alkene and then use H30+ to break it and it will form a trans diol
only way i know that will form a trans diol

and the cis ones u mention
KMNO4 cold, dilute + alkene-> cis diol (make sure its dilute and cold otherwise it will continue reacting and cleaving it into ketone and Carboxy acid)
1)OSO4/ 2)H202 +alkene -> cis diol

the alkene will go away after u react it.

 

[chessxwizard]

Keep in mind if you create an oxirane and then attack it with acid and water, the attack can occur at either side of the ring, creating a pair of enantiomers. If you want sterochemical specificity, go with KMnO4. 🙂

 

[CookieDough]

I understand your reasoning behind that, planar molecule, equal probability of attack from both sides, however epoxides are known to react with acid catalysts to form diols (glycols) via anti-addition. So no enantiomers here.

 

[rose786]

Keep in mind if you create an oxirane and then attack it with acid and water, the attack can occur at either side of the ring, creating a pair of enantiomers. If you want sterochemical specificity, go with KMnO4. 🙂

I thought an acid would attack an oxirane at the most substituted carbon, while a base attacks the least substituted. So if you're using either an acid OR a base, you wouldn't get mixed products.

 

[dontwakeme]

I thought an acid would attack an oxirane at the most substituted carbon, while a base attacks the least substituted. So if you're using either an acid OR a base, you wouldn't get mixed products.

You are correct. It all depends on whether the reaction is under basic or acidic conditions. Inversion of stereochem for both as well.

To the OP: OsO4 usually has pyridine with it.