[Rutherford]

What product will from in the cyclization reaction of the attached compound? I know that a nitrone moiety reacts in 1.3-dipolar cycloadditions, but what will add to it, as the product must have isoxazolidine and tetrahydrothiphene rings sharing a common bond (the two C atoms in the shared bond have S configuration, and the carbon connected to the oxygen has R configuration).

[discodermolide]

If you are thinking cycloaddition of the nitrogen, the obvious partner is the acetylene.
See if that fits.

[Rutherford]

But that doesn't give the required condensed heterocycles that the product has: isoxazolidine and tetrahydrothiphene.

[discodermolide]

How do you know the product contains these two heterocycles?

[Rutherford]

Here is the whole problem, without the historical background and the last part (E to F is the transformation I asked here). Maybe I mistaken with the initial compound:

[discodermolide]

I really wish you would post the entire question instead of bits and pieces
Have a study of this document, on page 2 is the synthesis referred to.
http://www.scripps.edu/baran/images/grpmtgpdf/Shenvi_Aug_03.pdf

Perhaps you could also start to use Google to find things, as I did here.

[Rutherford]

In the reaction where SOCl₂ is used, where does the ClCO₂- moiety come from?

[discodermolide]

I think the sulphur is missing.
Note the double inversion = retention of stereochemistry.

[Rutherford]

Yes. Thank you for the help.