The Dess‐Martin periodinane: 1,1,1‐triacetoxy‐1,1‐dihydro‐1,2‐benziodoxol‐3(1H)‐one intermediate: 1‐Hydroxy‐1,2‐benziodoxol‐3(1H)‐one 1‐oxide (1) product: 1,1,1‐Triacetoxy‐1,1‐dihydro‐1,2‐benziodoxol‐3(1H)‐one (2)

A highly convergent, enantioselective total synthesis of the aglycone of the tetrocarcins, (+)-tetronolide, is described. The synthesis highlights the use of several new methods, including camphor auxiliary-directed asymmetric alkylation and the enantioselective preparation of acyclic mixed acetals bearing chirality at the acetal center, and the highly efficient connection of the two major precursors via a ketene-trapping/intramolecular [4 + 2] cycloaddition strategy.

The syntheses of a variety of iminophosphonamide (PN2) ligands (2a−f), the corresponding hydrochloride salts (1a−c), and a number of bis(PN2) dichloride complexes of group 4 (3a−e) and their corresponding dialkyls (5a−e) are described. A novel monosubstituted PN2 “ate” complex 4 was prepared from ligand 2f and Zr(NMe2)4 on treatment with excess Me2NH·HCl. Piano-stool PN2 zirconium dichloride complexes 6a−h were accessible on treatment of CpZr(NMe2)3 (Cp = C5H5, Cp*) with PN2 ligands 2a−e, followed by metathesis with excess Me3SiCl or Me2NH·HCl (6a−g) or at low T with ethereal HCl (6h). Dialkyl derivatives 8a−h could be prepared from 6a−h or directly from ligands 2 and CpMMe3 (Cp = C5H5, Cp*; M = Ti or Zr). The intermediate Cp(PN2)Zr(NMe2)2, precursor to 6h, rearranged to the novel terminal difluoride complexes 7a,b at room temperature. A variety of complexes 3 and 6 or their corresponding alkyl derivatives have been characterized by X-ray crystallography. In addition, the novel “ate” complex 4 and difluoride complexes 7a,b have been structurally characterized in this manner. The structures of 7a,b in the solid state reveal strong, intramolecular coordination of the NMe2 group to the metal center, resulting in eight-coordinate complexes. One of these complexes is fluxional in solution, suggesting rapid exchange of bound versus free NMe2 groups coupled with the formation of coordination stereoisomers.

A short efficient enantioselective synthesis of both (+)- and (-)-saudin, a naturally occurring hypoglycemic diterpene, is described. This synthesis establishes the absolute configuration of natural (-)-saudin for the first time. The key steps include the enantioselective construction of a dimethyl Hagemann's ester by an asymmetric Michael reaction and establishment of the key 1,3 disposed quaternary centers by means of a novel Ti(IV) promoted Claisen rearrangement. The assembly of the polycyclic ketal skeleton was likely under kinetic control proceeding via formation of the C1oxygen-C7 bond through an oxonium ion intermediate in the final stage.