Ethers, aryl, deoxygenation

The deoxygenation of aryl 2-nitrophenyl sulphides with tervalent phosphorus compounds is analogous to that of the corresponding ethers except that in many cases the anticipated phosphoranes, e.g. (87), are thermally unstable.58 The extra stability of spirophosphoranes allows them to be isolated, e.g. (13), if cyclic phos-phonites are used in deoxygenation.8... 

Roush et al. have reported the synthesis of a durhamydn aglycon model (Scheme 1.39) [50]. Allylation of aldehyde 223 with the aUyhc borane 224 provided 225 after the formation of a xanthate. Deoxygenation gave the requisite RCM precursor whose cycUzation proceeded reasonably well provided that Ti(Oi-Pr)4 was used as an additive. As suggested by model studies, this additive may avoid the coordination of the rathenium carbene by either the aryl ether (OBOM) or the neighboring ethers (OMe, OTCE). 

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