Sodium epoxide ring opening with

Treatment of the /3-keto ester 220 with sodium ethoxide at elevated temperature triggered off an epoxide ring opening by / -elimination that was followed by the desired Knoevenagel condensation to afford the tricyclic product 206 (Scheme 34). The enone moiety in the intermediate 221 did not show a propensity for deprotonation and, therefore, the ketone carbonyl function of the enone moiety was available for a Knoevenagel condensation. The reduction of the p-keto ester (206) to the corresponding diol was the next objective. Treatment of the TES-protected -keto ester (TES-206) with DIBAH afforded the diastereomeric diols 222 and 223 in a moderate diastereoselec-tivity in favour of the undesired diastereomer 222. The diastereomers were separated and the undesired diastereomer 222 was epimerized to 223 by a sequence that consists of Mitsunobu inversion and benzoate ester reduction [98, 99]. 

The advantages of the catalyzed version are particularly apparent in the case of allyl alcohol whose epoxide, glycidol (2), is unstable to the catalyst.2 It can be obtained by catalyzed epoxidation at 0° with cumene hydroperoxide instead of t-butyl hydroperoxide in 65% yield and 90% ee. However, for use in a synthesis of the P-adrenergic blocking agent (2S)-propranolol (5), the epoxide is not isolated but treated with sodium a-naphthoxide to furnish the diol 3. The synthesis of 5 is completed by conversion to an epoxide (4) and ring opening with isopropylamine. 

It was shown that methyl 2,3-anhydro-/l-D-ribofuranoside (180) forms an equilibrium mixture with methyl 3,5- anhy dr o -/T i)- x y 1 oI uranoside (181), whereas the corresponding a anomer 182 gives in sodium methoxide solution the major product of epoxide-ring opening, namely methyl 2-0-methyl-a-D-arabinofuranoside (183).523,524... 

A convenient synthesis of cyclic P-ketophosphonates has been reported from sodium dialkyl phosphites and oc-nitroepoxides. The phosphite anions attack regiospecifically the carbon P to nitro group with epoxide ring opening and elimination of sodium nitrite. All the cyclic dialkyl P-ketophosphonates are isolated in good yields (56-96%, Scheme 7.50). 

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