STEREOSELECTIVE THERMAL REARRANGEMENT OF SYN-7-(1,2-BUTADIENYL)-1-METHYLBICYCLO[2.2.1]HEPT-2-ENE[SYN-7-(3-METHYLALLENYL)-1-METHYLNORBORNENE]

The synthesis and separate thermal rearrangements of (±)-(1 R*,4S*JS*)-7-[(R*)-1,2-butadienyl]-1-methylbicyclo[2.2.1]hept-2-ene (8a) and (±)-(1 R*,4S*,7S*)-7-[(S*)-1,2-butadienyl]-1-methylbicyclo[2.2.1]hept-2-ene (8b) are described. Both 8a and 8b are shown to rearrange to (i)-cis-1-ethylidene-3a,4,5,7a-tetrahydro-6-methylindene (9) and (±)-cj'j-1-ethy!indene-3a,4,5,7a-tetrahydro-3a-methylindene (10) with greater than 90% stereoselectivity. Epimer 8a gives predominantly (E)-9 and (Z)-10, whereas 8b gives predominantly (Z)-9 and (E)-10, results consistent with either a six-electron [σ2s + π2s + π2s] Cope or eight-electron [σ2s + π2s + (π2s + π2a)] augmented Cope process. Stereochemical assignments (8a vs 8b, (E)-9vs (Z)-9, and (E)-10 vs (Z)-10) are based upon experiments in nuclear Overhauser effect (NOE) difference spectroscopy. © 1990, American Chemical Society. All rights reserved.