Progress in the construction of cyclooctanoid systems: new approaches and applications to natural product syntheses.

Protection for the Hydroxyl Group, Including 1,2‐ and 1,3‐Diols

Toward a carbohydrate-based chemistry: progress in the development of general-purpose chiral synthons from carbohydrates.

Covering: 1 April 1998 to 30 June 1999. Previous review: J. Chem. Soc., Perkin Trans. 1, 1998, 4175.

Saturated oxygen heterocycles

Synthesis of the C11-C23 fragment of spirastrellolide A. A ketal-tethered RCM approach to the construction of spiroketals.

Base-promoted 1,2-shifts in α-benzyloxy ketones

The feasibility of alpha-ketol equilibration in a fully oxygenated B-ring setting for the rapid, enantioselective construction of an A/B bicyclic model related to Taxol has been examined. The key elements associated with this successful venture include selection of a proper array of protecting groups for the four hydroxyl groups present, suitable catalysis of the 1,2-pinacol-like shift, and an intrinsic dependence on the thermodynamic stabilities of the two alpha-ketol isomers. The key conversion of 13 to 14 is seen to be unidirectional and consequently to offer useful potential serviceability as more advanced thrusts toward Taxol are mounted.

Bicyclic Systems Related to Taxol. A Direct Means for Implementing C-2 Oxygenation and Demonstration of the Feasibility of alpha-Ketol Equilibration in a Fully Oxygenated B-Ring Setting.

Six transition-state models for intramolecular aldol C-ring annulation in suitably substituted bicyclo[6.2.1]undecanones have been defined. The first consideration is the inherent conformational flexibility of the nine-membered ketonic ring which does not limit effective deprotonation to a single C-8 epimer. When the oxygen substituents at C-4 and C-5 are not covalently linked, the configuration at C-5 defines the stereochemical course of the ring closure, with only the β series being amenable to the proper elaboration of paclitaxel. When C-4 and C-5 are incorporated into a 1,3-dioxane ring instead, the principal stereocontrol element is translocated into the aryl-substituted carbon of the cyclic acetal. To the extent that the Ar group remains equatorially disposed, then proper aldolization will materialize in only one of the four possible diastereomers. Experimental tests that are provided for three of the models are shown to conform to expectations. This analysis of the origin of stereoselectivity has, ...

Stereochemical Models for the Enantiocontrolled Construction of Fully Functionalized C Rings via Intramolecular Aldolization in Advanced Precursors to Paclitaxel

The Need for an Incisive Analysis of the Regioselectivity Associated with the Deprotonation of α-Alkoxy and α-Acyloxy Ketones

Heteroatomic Modulation of Oxyanionic Cope Rearrangement Rates. Consequences on Competing Nucleophilic Cleavage of an Oxetane Ring in Precursors to Paclitaxel

Qingbei Zeng

Papers

Base-promoted 1,2-shifts in α-benzyloxy ketones

Bicyclic Systems Related to Taxol. A Direct Means for Implementing C-2 Oxygenation and Demonstration of the Feasibility of alpha-Ketol Equilibration in a Fully Oxygenated B-Ring Setting.

Stereochemical Models for the Enantiocontrolled Construction of Fully Functionalized C Rings via Intramolecular Aldolization in Advanced Precursors to Paclitaxel

The Need for an Incisive Analysis of the Regioselectivity Associated with the Deprotonation of α-Alkoxy and α-Acyloxy Ketones

Heteroatomic Modulation of Oxyanionic Cope Rearrangement Rates. Consequences on Competing Nucleophilic Cleavage of an Oxetane Ring in Precursors to Paclitaxel