Tetrahydropyrans derived from pyranosides via substitution at Cl, i.e., C-glycopyranosides, occur as subunits of a variety of natural products1 and are of potential interest as chiral intermediates and enzyme inhibitors.2 Although stereoselective routes exist for both a-and ß-C-glycopyranosides,3 they suffer from low yields, poor selectivity, or lack of generality. Recent requirements related to our interest in the marine natural product palytoxin4 led us to seek a general expeditious route from simple starting materials.

Jin K. Cha received a B.S. degree in chemistry from Seoul National University in 1975. In 1981, he received his D.Phil. degree from University of Oxford, England under the direction of Professor Jack E. Baldwin. The first two years of graduate study were spent at Massachusetts Institute of Technology. After a two-year period of postdoctoral training under Professor Yoshito Kishi at Harvard University, he joined the faculty at Vanderbilt University in 1983. In Fall 1991 he moved to the University of Alabama where he is currently Associate Professor of Chemistry. His research interests include the development and applications of new methods and strategies for natural product synthesis.No-Soo Kim was bom in Seoul, Korea, in 1957. He obtained a B.S. degree in industrial chemistry from Hanyang University, and a M.S. degree in organic chemistry from Korea Advanced Institute of Science. In 1992, he received his Ph.D. in organic chemistry under the direction of Professor James D. White at Oregon State University. His Ph.D. dissertation involved synthetic studies toward trichothecene. After a postdoctoral study at the University of Alabama with Professor J. K. Cha, he joined Youngdong Institute of Technology as an Assistant Professor in Spring 1994. His research interests include the synthesis of biologically active compounds.be exploited to exert a unique stereodirecting effect on adjacent prochiral sp2 sites. In addition, the ready availability of optically pure allylic alcohols by enantioselective reduction of the corresponding ketones lends itself to practical asymmetric synthesis.2'3

NCN-pincer (S,S)-2,6-bis(4'-isopropyl-2'-oxazolinyl)phenyl-ligated rare-earth-metal dichlorides [(S,S)-Phebox-(i)Pr]LnCl2(THF)2 (Ln = Sc (1); Y (2); Dy (3); Ho (4); Tm (5); Lu (6)) were synthesized via transmetalation between [(S,S)-Phebox-(i)Pr]Li and LnCl3 in THF solvent. Interestingly, treatment of LaCl3 by the same method generated tris(ligand) lanthanum complex [(S,S)-Phebox-(i)Pr]3La (7). Molecular structures of complexes 1, 2, 3, and 7 were established by single-crystal X-ray diffraction study. Pincer ligand (S,S)-Phebox-(i)Pr adopts a κC:κN:κN' tridentate coordination mode to the central metal ion. Upon activation with [PhNHMe2][B(C6F5)4] and Al(i)Bu3, complexes 2-5 exhibited highly catalytic activities and more than 98% cis-1,4-selectivity for isoprene polymerization while complexes 1 and 6 were inactive for this reaction. When use of the catalyst system consisted of complex 2, [PhNHMe2][B(C6F5)4], and Al(i)Bu3 for isoprene polymerization, the resultant polymer has a high cis-1,4-selectivity up to 99.5%. The reaction temperature had little effect on the regioselectivity, and high cis-1,4-selectivity almost remained even at 80 °C.

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Metal homoenolates are characterized by the juxtaposition of an organometallic species b to a carbonyl group. These bifunctional reagents require a delicate balance between stability and reactivity for applications in C À C bond formations. A particularly useful class of homoenolates is zinc homoenolates. It is not surprising that known zinc and related metal homoenolates are limited primarily to those bearing weakly electrophilic esters, amides, and nitriles. [1,2] In contrast, little is known about zinc homoenolates of ketones and aldehydes because of the known proclivity of metal homoenolates to cyclize into the corresponding cyclopropoxides. [3] An attractive synthesis of cyclopropanols by treatment of a,bepoxy ketones with CH 2 (ZnI) 2 indeed corroborates facile cyclization of zinc keto homoenolates to the corresponding cyclopropoxides.[4] Nonetheless, we hypothesized that subsequent transmetalation with a suitable metal could shift the otherwise unfavorable equilibrium to generate b-keto homoenolates for subsequent elaboration [Eq. (1); M = metal]. As part of research programs on synthetic applications of the Kulinkovich cyclopropanation, [5,6] we report herein the preparation and in situ S N 2' alkylation of mixed zinc/copper keto homoenolates.Treatment of cyclopropanol with diethylzinc should result in formation of the zinc alkoxide A and ethane (Scheme 1). A could be in equilibrium with the homoenolate B, where the former is expected to be strongly favored. In situ trapping of B by transmetalation could afford D for subsequent reactions.

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The CO-displacement of [(mu-pdt)Fe(2)(CO)(6)] with (Ph(2)PCH(2))(2)N(n-Pr) in refluxing toluene gave an unsymmetrical chelating complex [(mu-pdt){Fe(CO)(3)}{Fe(CO)(kappa(2)-Ph(2)PCH(2)N(n-Pr)CH(2)PPh(2)}] (1) as a major product, together with a small amount of the symmetrical intramolecular bridging complex [(mu-pdt){mu-Ph(2)PCH(2)N(n-Pr)CH(2)PPh(2)}{Fe(CO)(2)}(2)] (2) and the intermolecular bridging complex [{mu,kappa(1),kappa(1)-Ph(2)PCH(2)N(n-Pr)CH(2)PPh(2)}{(mu-pdt)Fe(2)(CO)(5)}(2)] (3). In contrast, the reaction of [(mu-pdt)Fe(2)(CO)(6)] with (Ph(2)PCH(2))(2)NR (R = n-Pr, Ph) afforded the intermolecular bridging isomers 3 and 4 in the presence of a CO-removing reagent Me(3)NO.2H(2)O in CH(3)CN at room temperature. The molecular structures of 1, 3, and 4, as well as the doubly protonated complex [1(H(N)H(mu))](OTf)(2)] were determined by X-ray analyses. The protonation processes of 1 with HBF(4).Et(2)O and HOTf were studied in different solvents. The presence of the H(mu)...H(N) interaction in [1(H(N)H(mu))](2+) was studied by relaxation time T(1) and spin saturation transfer measurements. The mu-hydride of [1(H(mu))](+) and [1(H(N)H(mu))](2+) undergo facile deprotonation with aniline and rapid H/D exchange with deuterons in solution. In contrast, neither deprotonation nor H/D exchange was detected for [(mu-H)(mu-pdt){Fe(CO)(3)}{Fe(CO)(kappa(2)-dppp)}](+) ([5(H(mu))](+), dppp = Ph(2)PCH(2)CH(2)CH(2)PPh(2)) without internal base.

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