Regio‐ and Stereoselective Functionalizations of Tricyclo [3.3.0.0^2,8]octan‐3‐one, a Potential Synthon for Polycyclopentanoid Terpenes and Prostacyclin Analogs. Preliminary Communication

Abstract

SummaryChemical transformations of tricyclo [3 .3.0.02,8]octan-3-one (1) have been carried out in order to explore its potential utility as a versatile synthon for polycyclopentanoid terpenes and prostacyclin analogs. Various functionalizations of rings A and B and annulation of a third ring C were achieved in generally high yields. The system provides for a large measure of regio-and stereoselective reaction control.Introduction. -In the preceding communication [3] we described a facile and high-yield synthesis of tricyclo [3.3 .0.02~s]octan-3-one (1) and its methyl homologs 2 and 3, and the resolution of 1 into the pure enantiomers. Chemical transformations of I are now reported, which aim at the exploration of 1 as a synthon for polycyclopentanoid compounds such as 9 (0)-methanoprostacyclin (4), the pentalenolactone family (cJ: 5), and the coriolins (cJ 6)2). In particular, syntheses of the following intermediates have been achieved: (i) 9 in 67%, 12a in 79% and 12b in 55% overall yield from 1 (s. Scheme 2), all three possessing oxygen functions in ring A; (ii) 13 in 96%, 15 in 60% and 16 in 31% yield (Scheme 4), the ring B of 15 and 16 being alkylated and enlarged to a six-membered lactone; and (iii) 20 in 59% yield (Scheme 5 ) with a ring C annulated.

Nafion‐TMS‐ and TMS‐Trifluoroacetate‐Induced Rearrangements of Cyclopropyl Ketones ‐ A procedure for the regioselective conversion of semibullvalenes to barrelenes

“…With the first example (la; Scheme I , path i), a 1: 4 mixture of products 3a and Sa was obtained [4], evidently through reactions approximating an SN2 mode; in contrast, treatment of l a with methyl trifluoromethanesulfonate, trimethylsilyl trifluoromethanesulfonate or Nufion-TMS3) (path ii) gave exclusively 4a. We have suggested an intramolecular elimination to occur from 2, leading directly to the olefin 4a [2]. …”

“…64, Fasc. 8 (1981) ElNu in path i = CH3S020COCH3+ Br-or I- [4] ElNu in path ii = CF3S020CH3, CF$020Si(CH3)3, Nujion-TMS [2] ElNu in path iii= CF3C02Si(CH3)3…”

“…We have previously shown [2] [4] that the ring opening of the cyclopropane ring in these compounds can be effected by AcOMs3) or methyl and trimethylsilyl trifluoromethanesulfonates. In the case of AcOMs a cooperative action with additional nucleophiles such as Br-and I-can be observed.…”