Metal modified carbohydrates: syntheses of furanosylidene complexes and their aza analogues1

Synthesis and Uses of exo-Glycals

“…Suitable exo -glycals could be involved in a metathesis reaction with a given olefin to produce a new exo -glycal with different substituents. The reactivity of methylene derivatives has been tested by Dötz and co-workers in the reaction with Fischer diphenyl carbene to produce a new anomeric Fischer carbene. , Aminolysis of these complexes has been described, but other uses of these new species could be expected. The good reactivity of the exo -glycal double bond in a ring-closing metathesis has been attested by the construction of bicyclic systems from 2-olefinic substituted systems …”

Furanosylidene and Iminofuranosylidene Complexes: Synthesis by Stoichiometric Olefin Metathesis and Ring-Opening/Mitsunobu-Recyclization Sequence

“…Schakal plot of the molecular structure of complex 5. [21] One molecule out of two in the asymmetric unit is shown. Selected bond lengths [] and angles [8]: CrÀC-1 1.979(6), C-1ÀO-1 1.302 (7), O-1ÀC-4 1.483 (7), C-1ÀC-2 1.560 (7), C-2ÀC-3 1.502(9), C-3ÀC-4 1.527 (8); Cr ± C-1 ± O-1 125.0(4), Cr ± C-1 ± C-2 128.6(4), O-1 ± C-1 ± C-2 106.4 (5).…”

“…Metal carbenes 22, 25 and 26 represent a novel class of organometallic glycoconjugates which may be extended to iminoglycopeptides following the same ring-opening aminolysis/recyclization methodology. Moreover, this approach provides a general strategy complementary to the sugar lactam electrophile/carbonyl metalate nucleophile route; [21,47,48] it avoids the use of the tedious reducing agent potassium graphite, makes both N-deprotected and N-substituted iminofuranosylidene complexes accessible, and is compatible with the synthesis of carbohydrate-anchored azacyclopentylidene complexes. [49] We have described an efficient and multigram scale access to C-1-metal carbene modified furanoses and iminofuranoses which exhibit the characteristic properties of Fischer carbene complexes.…”

“…[15] Our aim is to activate the anomeric carbon of the carbohydrate skeleton by transforming it into a Fischer carbene centre, [1, 7, 16±19] with the aim of forming organotransition metal stabilized formal analogues of the ªglycosylidene carbeneº intermediates studied by Vasella and co-workers. [20] Herein [21] we report on an efficient synthetic access to furanosylidene chromium complexes and their application to novel organometallic glycoconjugates still bearing a metalcarbene functionality.…”

Cycloisomerization of Alkynols at Transition Metal Templates

“…[34] If DPPM is replaced by DPPE the hydroxyalkylvinylidene This route provides a complementary access to azacycloalkylidene complexes. [23] [41] The pentacarbonylmolybdenum-catalyzed cycloisomerization is also compatible with alkynyl-substituted carbon nucleophiles such as diethyl 2-(3-butyn-1-yl)-Scheme 9. The clopentylidene complexes by aminolysis to give an open-chain (γ-hydroxyalkyl)aminocarbene complex, which may subsequently undergo nucleophilic cyclization under Mitsunobu conditions [40] to afford 2-azacyclopentylidene complexes.…”