Constitutions are proposed for rubrenolide (Ia) and rubrynolide (Ib), two structurally novel natural products isolated from Nectandra rubra (Lauraceae). The trunk wood of the Amazonian tree, Nectandra rubra (Mez) C. K. Allen of the Lauraceae family has yielded rubrenolide and rubrynolide which represent a novel natural product type. Rubrenolide (Ia), C₁₇H₂₈O₄, m.p. 100°, [α]ᴅ + 21°, ν₍CO₎ 1746 cm⁻¹, was identified as a terminal alkene which, on the basis of i.r. and n.m.r. evidence, is associated with a -CH₂-CH=CH₂ group. Rubrynolide (Ib), C₁₇H₂₆O₄, m.p. 88°, [α]ᴅ + 21°, ν₍CO₎ 1746 cm⁻¹, was similarly shown to be the corresponding terminal alkyne containing a -CH₂-C≡CH group. On catalytic hydrogenation rubrenolide and rubrynolide each gave dihydrorubrenolide (Ic), C₁₇H₃₀O₄, m.p. 106-107°, [α]ᴅ + 22°. The two hydroxy groups present in rubrenolide were shown, using trichloroacetyl isocyanate, to be primary and secondary, and their vicinal relationship was established by periodate cleavage of dihydrorubrenolide which gave formaldehyde and an aldehyde, C₁₆H₂₇O₃, m.p. 60-53° (ν₍CO₎ 1760 and 1720 cm⁻¹). Intramolecular hydrogen bonding made a direct deduction of the lactone ring size in rubrenolide uncertain (vw 1745 cm⁻¹), but the acetonide, C₁₉H₃₂O₄, m.p. 47-48°, prepared from dihydrorubrenolide, acetone, and anhydrous copper sulphate was clearly a γ-lactone (ν₍CO₎ 1770 cm⁻¹). The C₁₇-skeleton of rubrenolide was determined by transforming dihydrorubrenolide to 4-methylhexadecane (III) by the sequence: (i) reduction (LiAlH₄), (ii) formation of a tetramesylate, and (iii) hydrogenolysis (LiAlH₄). Vigorous oxidation of rubrenolide with chromium trioxide in boiling acetic acid gave sebacic acid, HO₂C[CH₂]₈CO₂H. Thus, two possible constitutions (IIa) or (IIb) could be considered for rubrenolide, and a decision between these was possible on the following evidence. Mild oxidation of rubrenolide (CrO₃-HOAc; room temp.) yielded a vinylic (ν₍et₎ 1645, 990, and 910 cm⁻¹) lactonic acid (vw 1760 and 1700 cm⁻¹), C₁₆H₂₆O₄, m.p. 95-98° (IIc), whose n.m.r. spectrum showed an ABX system (Hₐ τ 7.05, Hᵦ τ 7.49, Hₓ m, τ ca. 7.0; J₍BB₎ 17.5, J₍Ax₎ 3.5, and J₍Bx₎ 8.5 Hz) which had to be associated with the oxidatively generated carboxy group (HO₂C-CHₐHᵦ-CHₓ<). A corresponding ABX system was also identifiable in the n.m.r. spectrum of the lactonic acid methyl ester (IId). These results established the constitutions of rubrenolide (Ia) and rubrynolide (Ib) and these proposals were fully confirmed by examination of the high resolution mass spectra and n.m.r. spectra of the two compounds and their derivatives. The assignment of seven ¹H multiplets observed in the 220 MHz n.m.r. spectrum (CD₃OD-D₂O) of dihydrorubrenolide (Ic) was made possible by spin-decoupling experiments. The branched chained C₁₇-compounds, rubrenolide (Ia) and rubrynolide (Ib) from Nectandra rubra (Lauraceae) show an interesting biogenetic relation to the family of structurally related linear C₁₇-compounds [e.g. (IVa) and (IVb)] recently isolated from the seed of the avocado pear, Persea americana (Lauraceae).