The First Asymmetric Synthesis of Optically Active Tropilidenes. Highly Regio- and Diastereo-differentiating Addition of Diazo Ester to Aromatic Ring Using 2,4-Pentanediol as Chiral Linking Bridge

Abstract

Optically active tropilidenes were prepared by cycloaddition of a diazo ester to an aromatic ring using 2,4-pentanediol as a chiral linking bridge under complete regio- and stereo-differentiations.

Stereoselective Cyclopropanation Reactions

“…Maguire recently investigated the diastereoselectivity in the intramolecular cyclization of chiral α-diazoketone derivatives of general structure 246 . , The ratio of diastereoisomers increased as the size of the β-substituent increased from Me to Et, Pr, and Bu (Table ). While an 89:11 mixture was obtained with the methyl group, only a single diastereoisomer could be detected with the isopropyl- and tert -butyl-substituted ketones.…”

Dirhodium(II) Carbenes : The Chiral Product Cascade

“…The high-yielding dirhodium(II) catalysed intramolecular reactions of α-diazocarbonyl compounds form the fused bicyclic cycloheptatrienes such as 56 This was reduced to the bicyclodecanone 57 with a determined enantiomeric excess of 33% equation 17 (Kennedy et al, 1990). Asymmetric success has also been observed using chiral dirhodium(II) phosphates 13a and have yielded enantioselectivities of up to 60% ee equation 18 (McCarthy et al, 1992 The only diastereoselective approach to aromatic cycloaddition involves the recent novel use of a chiral diol auxiliary as a tether between the aromatic substrate and the diazo reagent (Sugimura et al, 1998 Intramolecular aromatic substitution by metal carbenes represents a formal C-H insertion with tremendous potential for asymmetric synthesis via chiral catalysis. Although not many reports have appeared, there is evidence of early success.…”

Asymmetric Synthesis of Deoxypolypropionate Units via Stereoselective Hydrogenation of Optically Active Cycloheptatriene

“…3 The Bu ¨chner reaction is one of the successful examples that produces many chiral cycloheptatriene derivatives in optically active forms. 4 In the present study, we planned to use such a compound, 4, prepared from 3,5-dimethylphenol via the PD-tethered Bu ¨chner reaction of 5, to synthesize a chiral building block 1 (X ) H or OH) that corresponds to a deoxytripropionate unit (Scheme 1). A key step of this procedure is the hydrogenation of 3 at the conjugated diene to generate two (1)…”

“…Optically active 2,4-pentanediol (PD) is a popular chiral auxiliary and exhibits strict stereocontrollability when it is used as a tether connecting two reactants . The Büchner reaction is one of the successful examples that produces many chiral cycloheptatriene derivatives in optically active forms ).…”