Demetalation of Dicarbonyl(π-allyl)[hydridotris(pyrazolyl)borato]molybdenum Complexes via Lactonization

Abstract

Demetalation of dicarbonyl(π-allyl)[hydridotris(pyrazolyl)borato]molybdenum complexes can be achieved via lactonization. A carboxylic acid moiety is installed via addition of methyl phenylsulfonylacetate enolate to a diene−Mo(CO)2Tp complex, followed by desulfonylation and hydrolysis, so that the subsequent lactonization can be effected by CO/NO+ exchange or with iodine to give decomplexed products from cyclic and acyclic complexes.

Stereo- and Regiocontrolled Construction of Trisubstituted Piperidines Using a TpMo(CO)2(Dihydropyridine) Scaffold (Tp = Hydridotrispyrazolylborate)

“…The sequential, multistep, stereo- and regiocontrolled functionalization−demetalation of stoichiometric transition metal π-complexes has received considerable attention as a means of producing highly substituted organic molecules. − Stoichiometric π-complexes of molybdenum bound to polyene ligands are especially well suited to this task. ,, In this regard, hydridotris(1-pyrazolyl)borate (Tp) − used in place of the more commonly studied cyclopentadienyl (Cp) auxiliary ligand has significantly extended the applicability of the molybdenum-based methodology. ,,− In particular, the TpMo(CO) 2 ligand set has rendered useful the functionalization of a variety oxygen-containing heterocyclic systems. ,, Since the core units of a vast number of biologically active synthetic and natural products are nitrogen-containing heterocycles, the TpMo(CO) 2 -based synthetic methodology could prove of use in the stereocontrolled construction of these systems, also. To that effect, we report herein the synthesis, functionalization, and demetalation of a chiral, racemic TpMo(CO) 2 (dihydropyridine) complex and its use in the synthesis of 2,3,6-trisubstituted tetrahydropyridines and piperidines.…”

Lateral Stereocontrol Using π-Allylmolybdenum Systems: The Use of Methyl Substitution To Effect Conformational Control Leading to High Levels of Stereoselectivity

“…Within the last three years, our group has been successful in developing efficient synthetic routes toward a variety of new acyclic π-allylmolybdenum complexes, , in exploring the stereodirecting effect of molybdenum during functionalization, and in developing reliable methods of demetalation . In the present work, we have shown that functionalization of carbon−carbon double bonds and carbonyl groups adjacent to π-allylmolybdenum units is the result of the interplay between the directing effect of the metal and conformer populations, resulting in a 25:1 selectivity during double bond functionalization of complex 11 .…”

The Enantiomeric Scaffold Approach to Highly Functionalized 1-Oxadecalines: Enantio- and Regiocontrolled [4 + 2] Cycloadditions of 5-Alkenyl-η3-Pyranylmolybdenum Complexes

“…Iododemetalation ,, proceeded in good yield (84%) in the presence of excess of iodine to give diene 74 , most likely through elimination of hydrogen iodide from an intermediate unstable allylic iodide. Reduction of the ester group of 53 to the corresponding primary alcohol 75 was followed by activation of the TpMo(CO) 2 (allyl) moiety with NOPF 6 . ,− Subsequent intramolecular, Et 3 N-induced nucleophilic addition of the alcohol to the cationic allylmolybdenum complex and demetalation resulted in the dioxatricyclo product 76 in very good overall yield.

14 Demetalation Protocols for η-(3,4,4a)-Molybdenum [4 + 2] Cycloadducts a a Conditions: Protodemetalation [TFA (excess), CH 2 Cl 2 , rt, 20 min].

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