(1R,3S,6S)-6-tert-Butyl-1-hydroxymethyl-5-methoxy-6-methyl-7-oxa-4-azaspiro[2.5]oct-4-en-8-one and dimethyl [(1S,1'R,3'S,6'S)-(6'-tert-butyl-5'-methoxy-6'-methyl-8'-oxo-7'-oxa-4'-azaspiro[2.5]oct-4'-en-1'-yl)hydroxymethyl]phosphonate. 
The molecules of the title compounds, C(13)H(21)NO(4), (I), and C(15)H(26)NO(7)P, (II), are linked into chains along the c direction in (I) and along the b axis in (II) through O-H.O hydrogen bonds.  The heteroatomic ring in (I) adopts a twist-boat conformation, while that in (II) has a conformation intermediate between boat and twist-boat.  The P atom has a distorted tetrahedral geometry.