(1R,2'S,6S,9a'S)-6-(benzyloxymethyl)-2'-((triisopropylsilyloxy)methyl)-6',7',8',9a'-tetrahydro-2'H-spiro[cyclohex[3]ene-1,9'-pyrido[2,1-b][1,3]oxazin]-2,4'(3'H)-dione