Highly strained C-C bonds: 3-(1 '-hydroxy-4 '-isopropyl-2 ',2 '-dimethyl-1',2 '-dihydrobenzocyclobuten-1 '-yl)-3-methyl-2-butanone ethylene acetal, (I), and (3S*,1 ' S*)-3-Acetoxy-2-(1 '-hydroxy-1 ',2 '-dihydrobenzocyciobuten-1 '-yl)-2-methylpentane, (II)

The crystal structures of the title compounds, C20H30O3 tl, and C16H22O3 (I I), are described. The benzocyclobutene rings in (I) and (II) are approxima tely planar. The lengths of the Csp(3)-Csp(3) bonds in the cyclobutene ring s of (I) and (II) are 1.659 (2) and 1.596(2) Angstrom, respectively, The C- C bond elongation observed in (I) may be ascribed to steric congestion and/ or electronic effects on the bond exerted by the methyl groups and the alky l side chain attached to the cyclobutenol moiety, together with a ring stra in expected for a four-membered ring system.