A Versatile Synthetic Platform Based on Bicyclo[4.1.0]heptenes

An enyne cycloisomerization/[5+1] reaction sequence to synthesize tetrahydroisoquinolinones from enyne-enes and CO

An enyne cycloisomerization/[5+1] reaction sequence was developed to synthesize tetrahydroisoquinolinones from linear enyne-enes and CO. The first step is a gold(i)-catalyzed enyne cycloisomerization, generating six-membered-ring-fused vinylcyclopropanes. The second step is a rhodium(i)-catalyzed [5+1] reaction of vinylcyclopropanes with CO. This two-step reaction could also be carried out in one-pot without isolating the cycloisomerization product generated from the first step of this sequence.

Atropisomeric [(diphosphine)Au2 Cl2 ] complexes and their catalytic activity towards asymmetric cycloisomerisation of 1,6-enynes

X-ray crystal structures of two [(diphosphine)Au2 Cl2 ] complexes (in which diphosphine=P-Phos and xylyl-P-Phos; P-Phos=[2,2',6,6'-Tetramethoxy-4,4'-bis(diphenylphosphino)-3,3'-bipyridine]) were determined and compared to the reported structures of similar atropisomeric gold complexes. Correlations between the Au⋅⋅⋅Au distances and torsional angles for the biaryl series of ligands (MeOBIPHEP, SEGPhos, and P-Phos; BIPHEP=2,2'-bis(diphenylphosphino)-1,1'-biphenyl, SEGPhos=[(4,4'-bi-1,3-benzodioxole)-5,5'-diyl]bis[diphenylphosphine]) can be made; these measurements appear to be very dependent upon the phosphorous substituent. Conversely, the same effect was not observed for ligands based on the binaphthyl (BINAP) series. The catalytic activity of these complexes was subsequently assessed in the enantioselective cycloisomerisation of 1,6-enynes and revealed an over-riding electronic effect: more-electron-rich phosphines promote greater enantioselectivity. The possibility of silver acting as a (co-)catalyst was ruled out in these reactions.