During a synthetic work on &&-muscone (11, we have investigated the condensation reaction of cycloalkanones I and d,d-dlchlorolsobutylene to flnd out that this reaction provides substantial amounts of the tltle oompounds II in addltlon to the deslred blcycllc products. The current lntereet in bloyolo-(3.3.l)nonane system (2) prompts us to record our preliminary results lnaludlng some reactions of II. Condensation of cyclotrldeoanone (Ia) (3) with two moles ofol,d-dlchlorolsobutylene (4) was carried out In the presence of excess sodium hydride in toluene at 90-1000 for 40-50 hrs to afford IIa, m.p. 69.5-700, in a 26% yleld. ,This structure followed from an elemental analysis (5) and spectral results; IH (Nujol): 1710 (C=C), 3080, 1650, 880 cm" (=CH,); NMFt (Ccl,): s 4.67 g (4 H, oleflnlc protons), 2.47 distorted AB-quartet (8 H, oyclohexane rlng protons, sA-& = ca. 0.14, J = ca. 15 Hz), 1.8-0.7 _m (20 H, deoamethylene protons): UV (g-hexane): f(220 nm) = 2800, Emln(268 nm) = 8, f,,(305 nm) = 32. The possible existence of methyleneayolobutane moieties such as in III was ruled out by the oxldative cleavage of exo-double bonds. -Thus, hydroxylatlon with KMnO, followed by treatment wlth Pb(OAc), gave IV (5) In a 13% yield; m.p. 176-1780; IH (Nujol): 1730, 1710 cm-l (C=O, no cyolobutanone); NMR (CDCl,): $2.70 A&quartet (8 H, gA-& = 0.31, J = 15 Hz), 2.1-1.0 2 (20 H). Upon perlodatepermanganate oxldatlon (6), the dlene IIa afforded an oxaadamantane V (5) in a 78% yleld: m.p. 174-175O (dec.): IR (Nujol): 3250 (OH), 1710 (C=C), 1110, 980 cm" (C-O). Dehydratlon of V lnto IV was effected by means of E-toluenesulphonlo acid and molecular sieves In tetrahydrofuran, whereas IV was reconverted into V on