1-Oxa-6-azaspiro[4.5]decane-6-carboxylic acid, 2-[(2R,4S)-3,4-dihydro-4-methyl-6-(trimethylstannyl)-2H-pyran-2-yl]-8,10 -dimethyl-3-[(triethylsilyl)oxy]-, 2-(trimethylsilyl)ethyl ester, (2R,3R,5S,8