p-Toluenesulfonic acid → Diethyl 1,4-dioxaspiro[4,4]nonan-2,3-dicarboxylate

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Example 4 was repeated in which the DTDR was replaced by an equivalent amount of DODDR and the DIOP was replaced by an equivalent amount of (-)-2,3-bis(diphenylphosphinomethyl)-1,4-dioxaspiro[4,4]nonane, prepared by: (a) reacting L-(+)-diethyl tartrate with cyclopentanone in benzene in the presence of p-toluenesulphonic acid to give diethyl 1,4-dioxaspiro[4,4]nonan-2,3-dicarboxylate, b.p. 154°-158° C./6.0 mm., (b) reducing this with lithium aluminium hydride to give (-)-2,3-O-cyclopentylidene-L-threitol, b.p. 124°-130° C./0.2 mm., (c) converting this to (-)-1,4-ditosyl-2,3-O-cyclopentylidene-L-threitol m.p. 109°-115.5° C. by reaction with p-toluenesulphonyl chloride in pyridine and (d) treating with potassium and diphenylphosphine in tetrahydrofuran to give the desired compound m.p. 93°-95° C.

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