Hydroxylation of Alkenes

[maverick280857]

Hi

I need some help with the following reactions:

1. cis-1-phenyl-but-1-ene + osmium textroxide + aq sodium bisulfite
2. trans-1-phenyl-but-1-ene + osmium tetroxide + aq sodium bisulfite

To make things simpler, I am attaching a diagram which includes my solution. Reaction 2 is clear to me but I think another product should be formed in the first reaction according to the principle that if a stereogenic center is created in a reaction, all configurations about it are formed. Is this reasoning correct?

Thanks for your help.

Cheers
Vivek

[movies]

Yes, your reasoning is correct. The product that you have drawn would come from the osmium attacking the top face of the alkene as you have it drawn. The enantiomer of the product you have drawn could be formed by the osmium attacking the bottom face of the cis compound you have drawn.

[chem_tr]

Dear friends,

I am not sure about reaction two, as osmium tetroxide (in the presence of an oxidizing agent such as sodium bisulfite) always produces syn- type of compounds, I mean, trans-alkenes with bulky groups will even give syn- diols; so there will not be any chiral compound except that the olefin is located at the terminal. In that case, a vicinal diol is produced with one chiral carbon.

Please view my figure in the attachment, taken from Francis Carey's Organic Chemistry, 1987, ISBN: 0-07-009831-X, from pages 570 and 571.

By the way, your reasoning is true about stereogenic centers, Vivek. Movies is right also, about attacking topwards and bottomwards through an alkene; however, I'm not sure if it is valid for osmium tetroxide as it forms a complex compound.

Regards,
chem_tr

[movies]

The "syn" terminology tends to fail in straight chain cases because it is dependent on how the compound is drawn. Maverick's picture shows the products in Newman projections, where the horizontal groups are, by convention, protruding out of the plane of the page. I think that if you inspect the image again carefully with this in mind you will find that the image is of the correct racemic product from the trans olefin. Indeed the transition state is as you described, chem_tr, and the initial osmate ester does exist with both oxygens on the same side of the olefin. However, once the osmate ester is cleaved the C-C bond between the hydroxyls can rotate freely and attain a conformation like Maverick drew.

[maverick280857]

Thanks again chem_tr and movies for all your help.

Cheers
Vivek