Formation of Steroidal Skeleton From Resin Acid

Abstract

Dehydroabietic acid (1) was converted into 14 and 20 having the steroidal skeleton, by the use of its isopropyl group for the formation of the steroidal d-ring.

Total synthesis of halogenated monoterpene marine natural products via the Diels-Alder reaction

“…Qualitatively, a similar rate difference was observed for the reaction of 5 or 6 with butadiene (7) or with isoprene (8); i.e., 5 undergoes cycloaddition faster than 6. A quantitative assessment of the rate difference in the isoprene reactions is difficult because of the additional complication of regioisomeric products.…”

“…This observation was confirmed by monitoring separate small-scale reactions of 5 and 6 with butadiene under identical conditions by NMR. A surprising result obtained from this NMR experiment is that formation of the cycloadduct 10, by reaction of 5 with butadiene, proceeds at a rate somewhat faster than the formation of the cycloadduct 11 from butadiene (7) and the /3-haloacrolein 6 (vide infra).…”

“…We had noted previously that the cis dienophile 5 is almost quantitatively converted into the trans dienophile 6 by trace acid catalysis,8® In the absence of an acid scavenger, the reaction of 5 with butadiene (7) yields a mixture of cycloadducts 10 and 11 due to isomerization of 5 to 6 before cycloaddition occurs. In order to avoid this undesirable isomerization by traces of acid liberated by dehydrohalogenation of a cycloadduct or by cyclocondensation of the /3-haloacroleins (5 or 6) with themselves,10 propylene oxide was added to each of the cycloaddition reactions as an acid scavenger.…”

“…The two /3-dienophiles which we studied are cis-and irans-3-chloro-2-methylpropenals (5 and 6). Compound 5 is prepared by a procedure previously described by us and has been utilized in the total synthesis of costatolide and costatone.8 Compound 6 is obtained by the Vilsmeier-Arnold-Haack reaction of propionaldehyde with a chloromethylene iminium salt.9 We compared the [4 + 2] cycloaddition reactions of the two aldehydes 5 and 6 with three simple dienes: butadiene (7), isoprene (8), and cyclopentadiene (9). All cycloaddition reactions were carried out in a sealed tube in toluene solution at 150 °C over a period of 24 h. The products obtained for these cycloaddition reactions, the isomer distributions, and the yields are summarized in Figure 2.…”

“…Our alcohol 40 has similar spectral characteristics indicative of the same regio and stereochemical assignments as those for violacene, i.e., 4.16 (dd, J = 4.3, 12. 7 Hz, 1 H, (-CHC1-)), 3.76 (dd, 1 H, J = 3.8,12.0 Hz, 1 H, (-CHC1-)), 2.22 (ddd, J = 12.4, 12.7, 12.0 Hz, 1 H, (-CH2-)), and 2.57 (ddd, J = 4.3, 3.8, 12. 4 Hz, 1 H, (-CH2-)).…”