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Four-membered heterocycle-derived carbenes

Starting from (silyl)(phosphino)diazomethane derivatives, stable pseudo-diazoalkenes and carbenes have been obtained. The diazomethylenephosphoranes are very reactive dipolarophiles but are also synthetic equivalents of naked carbon C . The stable carbenes react in a similar manner to their transient analogues, but also exhibit new reactions the synthesis of unsaturated three-membered heterocycles is particularly noteworthy. Ring expansion reactions involving the latter are of special interest since they afford novel non-antiaromatic four-7t-electron four-membered heterocycles. [Pg.233]

Carbenes Derived from Four-membered Heterocycles... [Pg.15]

Diverse N-heterocyclic carbenes containing Lewis-acidic boron atoms within the carbene ring have been described in the literature. Carbene 128 derived from a four-membered heterocycle (Figure 1.11) showed several similarities with the previously discussed carbene 77b (see Scheme 1.11). Substitution of the... [Pg.27]

The simplest stable singlet carbene derived from a cyclic precursor is cyclo-propylidene. Like other carbocyclic carbenes, it does not contain a heteroatom within the ring and is therefore not further discussed here. The first cyclic carbene based on a four-membered heterocycle was described in 2004. Deprotonation of iminium salt 87a with KHMDS gave carbene dimer 88a=88a while the same reaction with 87b, bearing even bulkier N,N -substituents, led to the isolation of 88b (Scheme 1.11). Attempts to deprotonate 87a with KOt-Bu resulted in the opening of an endocyclic P-N bond, demonstrating the electrophilic character of the phosphorus atom in this compound. [Pg.43]

Stable free carbenes derived from four- (13), six-, or seven-membered heterocycles 14 are also known. Carbenes of type 13 can possess a phosphorus [19] or a boron atom [69] within the heterocycle. These carbenes exhibit extreme values regarding their NMR spectroscopic ( carbene-c 285 and 312.6 ppm) and structural properties (angle N-Ccarbene-N 96.72(13) and 94.0(2)°). [Pg.102]

Summary Trimethyl- and triisopropyl-silyl diazomethane derivatives have been used for the synthesis of new types of diazo derivatives including those featuring a heavier main-group element or a transition metal directly bound to the diazo-carbon. They are also precursors to a variety of stable nitrilimines and carbodiimides, and stable pseudo-diazoalkenes and carbenes. (Phosphino)(silyl)carbenes have been used in the synthesis of new types of heterocycle including some stable four-7c-electron four-membered derivatives. [Pg.223]

Most of the known N-heterocyclic carbenes are derived from five-membered heterocyeles with additional oxygen, sulfur or phosphorus heteroatoms. Stable NHCs with up to four heteroatoms and saturated or unsaturated five-membered heteroeyeles are discussed in the following Section. [Pg.16]


See other pages where Four-membered heterocycle-derived carbenes is mentioned: [Pg.106]    [Pg.98]    [Pg.106]    [Pg.98]    [Pg.147]    [Pg.6]    [Pg.32]    [Pg.56]    [Pg.26]    [Pg.326]    [Pg.146]   
See also in sourсe #XX -- [ Pg.15 ]




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Carbenes Derived from Four-membered Heterocycles

Carbenes heterocyclic

Derived members

Four-membered

Four-membered heterocycle-derived

Four-membered heterocycles

Heterocyclic carbene

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