Retrosynthetic analysis Wittig reaction

The vitamin D3 metabolite la,25-dihydroxycholecalciferol is a lifesaving drug in treatment of defective bone formation due to renal failure. Retrosynthetic analysis (E.G. Baggjolint, 1982) revealed the obvious precursors shown below, a (2-cyclohexylideneethyl)diphenylphosphine oxide (A) and an octahydro-4f/-inden-4-one (B), to be connected in a Wittig-Homer reaction (cf. section 1.5). 

With a target chosen, the next task was a retrosynthetic analysis (Scheme 2). We envisioned attaching the C(12-16) side chain of 1 via a Wittig reaction of tricyclic aldehyde 4. We envisioned the lactone of 4 as being prepared by cyclization of a cyano alcohol, which could be prepared from diester 5. Finally, we presumed that the C(18) Me group of 5 could be installed by addition of MeLi to the (3-ethoxyenone group of 6. Our retrosynthetic analysis ended at this point, because 6 was very similar to... 

Applying retrosynthetic analysis, the presence of the alkene group in the target suggests using a Wittig reaction in its preparation. 

Determine the Starting Materials for a Wittig Reaction Using Retrosynthetic Analysis... 

Our retrosynthetic analysis is shown in Scheme 18. Retro-Wittig reaction leads to aldehyde 105 which is generated from alcohol 106 by Swem oxidation. This tetrahy-drofuran system might be generated by ring closure of epoxy alcohol 107 although this would involve an SN2 type attack of the hydroxyl function at the more hindered position of the epoxide. The diol unit in 107 was to be created by osmylation of an allylic alcohol as represented by precursor 108 (8). 

With this new approach in mind, the revised retrosynthetic analysis would utilize two different Wittig reactions to homologate the carbon side chains, providing ketoolefm (+)-16 (Scheme 13). Further disconnection revealed hydroxy aldehyde (+)-27 which could arise from a selective DIBALH reaction of lactone (+)-28. Applying Bringmann s method, lactone (+)-28 would be enantiomerically enriched via a kinetic resolution of a racemic lactone mixture. Racemic lactone ( )-28 could arise from a... 

Synthesize 2-methyl-1-phenylprop-l-ene using a Wittig reaction. Begin by writing a retrosynthetic analysis. 

Wittig reactions, and reactions related to it, are used for the regiospecific synthesis of alkenes from aldehydes and ketones. Their retrosynthetic analysis begins with disconnecting the double bond as shown and introduces a novel stmctural type called an yiide. 

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