Structure spirocyclic

The only structurally characterized derivative of a trisimido organophos-phonate anion is the spirocyclic tellurium(IV) complex (19), which is obtained from the interesting redox reaction between PhPCl2 and [Li2Te(N Bu)3 ] 2 [27]. The phosphorus(V)-centered ligands are generated by imide transfer from tellurium to the phosphorus(III) atoms with concomitant reduction of one-half of the tellurium in the Te(IV) reagent to elemental tellurium [27]. 

A crystal structure is available for the compound with R = HC=C(CH2)2, and a mechanism was also proposed. On changing the reaction conditions (CH3CN, 82°C) and using Af-propionylimidazole, a tricyclic imidazo[l, 2 l,2]pyrrolo[2,3-6]furan was obtained in a diastereoselective spirocyclization reaction tl59],[157]... 

Pavan Kumar et al. <2006NJC717> investigated the reaction of diethyl azodicarboxylate (DEAD) or diisopropyl azodicarboxylate (DIAD) with cyclic phosphates or phosphoramides in order to determine the structural preferences in spirocyclic penta- and hexacoordinate aminophosphoranes. They found that sulfur would coordinate to phosphorus to form the [3.3.0] bicyclic compounds 94-96. 

Lithium halides disrupt the dimeric structures of 59a or 59c to give distorted cubes of the type 60, in which a molecule of the lithium halide is entrapped by a Li2[E(NtBu)3] monomer.164,165 Similar structures are found for the MeLi, LiN3 and LiOCH=CH2 adducts of 59a.166 168 The pyramidal dianion [Te(N Bu)3]2 has a rich coordination chemistry,169 171 although redox processes are sometimes observed in metathetical reactions with metal halides. For example, reaction with PhPCl2 gives a spirocyclic Te(IV) complex of the [PhP(NtBu)3]2 dianion,163 while treatment with Sn(II) salts generates a complex with a four-coordinate Sn(IV) = Te functionality.172... 

An intramolecular imino-ene reaction was used as the key step in the synthesis of the non-natural perhydrohis-trionicotoxin.90 The spirocycle 147 was obtained as a single diastereomer upon exposure of 145 to TiGl2(01Pr)2 (Scheme 31). The transition structure 146 was proposed to explain the high diastereoselectivity of this reaction. 

Phenyl-[l,3]dioxane 32 has been reported to bind the 0X2 receptor with a pX of 8.3 and a pXb of 7.9, and is 600-fold selective for 0X2 over 0X1 [85,86]. JNJ-10268752 (no specific structure has been disclosed) has been described as a selective 0X2 receptor antagonist (X, 0X1 /OX2 = 18/2, 500 nM, respectively) [87]. Compounds exemplified by 33 have been reported as 0X2 receptor antagonists (IC5o = 9nM) selective versus 0X1 (IC50 = 1870 nM) [88]. Recently, open chain amide 34, sulfonamide compound 35 [89,82], and spirocyclic sulfonamide 36 [90]... 

Perhaps the most interesting arthropodan defensive compounds from the point of view of structural diversity are the alkaloids. While alkaloids had long been believed to arise only as a consequence of plant secondary metabolism, it has become apparent over the last few decades that arthropods are both prolific and innovative alkaloid chemists. The millipede Polyzonium rosalbum, once thought to secrete camphor (20), in fact gives off a camphoraceous/earthy aroma produced by the spirocyclic isoprenoid imine polyzonimine (21). 

Tacke et al. have reported a new family of spirocyclic silicates adopting betaine-type structures of the general formula X4SiCH2NR2H (X = electronegative atoms or groups R = organic groups) in which the silicon atoms are... 

Pseudorotation.—A number of spirocyclic phosphoranes possess square-pyramidal structures rather than the trigonal-bipyramidal structures previously assumed, and this could have important consequences on the interpretation of their variable-temperature spectra. There is, as yet, no evidence that acyclic or monocyclic phosphoranes favour the square-pyramidal geometry, and the variable-temperature XH... 

A third alkaloid of this type, chilocorine B (20), was isolated from C. cacti. In this molecule, NMR experiments showed that the 2-methylperhydro-9i -aza-phenalene and the 3,4-dimethyloctahydro-8b-azaacenaphtylene subunits are linked in a spirocyclic fashion. An X-ray diffraction analysis fully determined the structure and relative stereochemistry of this alkaloid [34]. 

The molecular structure of 124 has been elucidated by an X-ray structural analysis. The central structural motif of 124 is an unsymmetrically substituted six-membered TisOs ring. Two pentamethylcyclopentadienyl ligands are coordinated to one titanium atom, while the other two are free of Cp. They are both part of eight-membered TiSi304 ring systems within the silsesquioxane frameworks. This results in an unusual bis(spirocyclic) inorganic ring system in the molecular structure of 124. 

Scheme 17.26 Generation of a novel spirocyclic structure by indole oxidation.

Spirocyclic C-aryl glycosides are central structural skeletons of papulacandins that constitute a family of novel antifungal antibiotics isolated from a strain of Papularia sphaerosperna. They have shown potent in vitro antifungal activity against Candida albicans, Candida tropicalis, Pneumocystis carinii, among other microorganisms [110],... 

Fig. 12. Molecular structure of a novel spirocyclic compound, (from Ref. 357)...

It has long been recognized that nitrone cycloadditions may allow access to spirocyclic ring systems. Such systems are inherently difficult to synthesize by conventional methods, yet are a structural component of a number of biologically active natural materials. Two common strategies have emerged for spirocycle generation from exocyclic or endocyclic nitrones (Scheme 1.45). In the exocyclic version, the carbon atom (arrowed) of the nitrone C=N double bond of dipole 209 carries a cyclic substitutent and thus an intermolecular cycloaddition reaction will... 

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