Aliphatic semidiones. XV. 2,3-Semidiones derived from the bicyclo[n.1.0]alkanes

Free-Radical Rearrangements

“…Genera tion of a deuterium-labeled radical revealed a more rapid sigmatropic shift (269-°-270). Thus, the rearrangement of 274 to 276 is believed to proceed via electrocyclic reactions of the radical dianion 275 (485). A more complex example or apparent valence isomerization is provided by the rearrange ment of 273 (483).…”

Chemistry of carbanions. 33. Use of intramolecular alkylation for the stereospecific formation of a cis-decalone

“…When the XH NMR spectrum of ketone 5b was rerun at 100 mHz to examine the pattern attributable to the CHCO multiple! at 2.4-2.6, we obtained partial resolution into three closely spaced lines at 248,250.5, and 253 Hz; the width at half-height of the envelope containing these peaks was 10 Hz. This observation is compatible with our assigned stereochemistry in which the COCH proton is equatorial and is coupled with two equatorial and one axial adjacent protons (typical J values all 2-3 Hz).…”

“…NMR (CCD 3.37 (2 H, t, J = 7 Hz, CH2Br), 1.0-2.6 (14 H, m, aliphatic CH including a CHgCO singlet at 2.10), and 0.82 (9 H, s, t-Bu); mass spectrum, m/e (rel intensity) 290 (M+, 0.5), 288 (M+, 0.5), 209 (11), 153 (12), 123 (10), 109 (18), 95 (10), 81 (11), 71 (23), 57 (71), 55 (12), 43 (100), and 41 (29).…”

“…In such cases, including reactions with olefins 5 at 25 °C, the desired addition of a Br• radical to the double bond competes with abstraction of the allylic H atom by Brto form an allylic radical such as 8.5a•6 Subsequent reaction of this allylic radical 8 with more HBr can either form a mixture of terminal olefins 5 and 6 or the structurally isomeric olefin 9; free-radical chain addition of HBr to this olefin mixture 5,6, and 9 then forms both the desired bromo ketones 7 and the unwanted isomers 10 and 11. Thus, this competitive H-atom abstraction is clearly undesirable because it forms synthetic intermediates with either the wrong stereochemistry (11) or the wrong structure (10). Since free-radical addition reactions typically have a lower activation energy than free-radical atom abstraction reactions,6-7 there was reason to expect that the importance of the competing H-atom abstraction reaction (to form 8) could be diminished by lowering the reaction temperature.…”

Aliphatic semidiones. XVI. Semidiones derived from the bicyclo[n.1.1.]alkanes

“…After removal of the solvent under reduced pressure, the residue was dissolved in 150 ml of ether and the resulting solution was washed with dilute hydrochloric acid followed by 10% sodium bicarbonate. The solution was dried over MgSD4 before removal of the solvent under reduced pressure to yield 5.9 g (58%) of the crude diester, >90% pure by glpc: ir (neat) 1730 cm'1; pmr (CC14) 1.55-3.15 (m, 6), 3.61 (s, 6); mass spectrum (70 eV) mfe (rel intensity) 186 1), 155(36), 154 (11), 127 (14), 126(23).…”