Paul Müller

As an approach to the enantioselective synthesis of trans-decahydroquinolines (DHQs), desymmetrization of meso-aziridine (5) with various carbon nucleophiles under catalytic conditions was investigated. By applying TMSCN in the presence of YbCl₃ and chiral non-racemic ligands, nitrile 13 was obtained with an ee up to 40%. Nitrile 13 was a key intermediate in a novel route to trans-DHQs.

The cyclopropanation of dihydrofuran and dihydropy­ran with methyl 1-(silanyloxy)vinyl diazoacetates in the presence of chiral Rh(II)-catalysts affords cyclopropanes with high diastereo- and enantioselectivitiy. The cyclopropanes, in turn, rearrange to ­dihydrofurans upon desilylation with TBAF.

Olefins are cyclopropanated with dimethyl malonate (1a) iodosylbenzene (PhIO) and a Rh(II) carboxylate catalyst via an in situ generated phenyliodonium ylide (1c). Enantioselectivities of up to 90% for 4-bromostyrene and 98% for pent-1-ene have been observed with (S)-N-4-bromo-1,8-naphthanoyl-tert-leucine (4c) as the chiral ligand. The same catalyst was effective for olefin cyclopropanation with Meldrum's acid, giving cyclopropanes with 96% (with styrene) and 87% ee (with pent-1-ene), respectively.

The cyclopropanation of styrene with (silanyloxyvinyl)diazoacetates proceeds with exceptional diastereo- and enantioselectivity in the presence of chiral Rh(II) catalysts. 1,8-Naphthoyl-protected amino acids are the most effective Rh(II) ligands for these transformations.

Phenyliodonium ylides, readily available upon treatment of CH-acidic compounds such 1,3-dicarbonyl derivatives with iodobenzene diacetate, react in the presence of rhodium(II) or copper catalysts to afford products derived from carbenoid pathways. Chemo- and enantioselectivity of the reactions are identical to those of the corresponding diazocompounds, indicating metallocarbene intermediates with both precursors. An exception to this occurs in the intramolecular cyclopropanation of phenyliodonium ylides, where a competing uncatalyzed pathway intervenes at room temperature. When phenyliodonium ylides are generated in the presence of Rh(II) catalysts and olefins, they react in situ to afford cyclopropanes.