Spiro positions

P nuclear magnetic resonance (NMR) spectroscopy has been of great use in determining the coordination state and stereochemistry of the phosphorus atom at the spiro position in spirophosphonia compounds, spirophosphoranes and spiroperphosporanides. The 31P chemical shift is also sensitive to the nature of the atoms directly bonded to the spiro phosphorus center and the size of rings of the spirocyclic system. 

Alternate to Rules A-41.1 and A-41.2)—When two dissimilar cyclic components are united by a spiro union, the name of the larger component is followed by the affix spiro which, in turn, is followed by the name of the smaller component. Between the affix spiro and the name of each component system is inserted the number denoting the spiro position in the appropriate ring system, these numbers being as low as permitted by any fixed enumeration of the component. The components retain their respective enumerations but numerals for the component mentioned second are primed. Numerals 1 may be omitted when a free choice is available for a component. 

Phenyl-6-nitroBIPS was easily resolved (at the 3 -carbon atom, not the 2 -spiro position) by reaction in ethanol with either (+) or (-) 10-camphorsulfonic acid. The first fraction to crystallize in each case was the salt of the open form. Both salts had a mp of 237°C and their solutions, after standing to thermally equilibrate at the 2 -carbon atom, showed equal but opposite rotations, [oc]d25 = -201° for the salt from the (+) sulfonic acid and +201° for the salt from the (-) acid. After treatment of these salts with aqueous sodium acetate and benzene, the respective spiropyrans, having melting points of 201-202°C and specific rotations of -11° and +11° for thermally equilibrated solutions, were recovered from the benzene extract. Similar attempts to resolve several other 3 -phenylBIPS with the camphorsulfonic or 3-bromocamphor-8-sulfonic acids were only pardy successful.7... 

Compounds with phosphorus at the spiro position 01MI29. 

It has been demonstrated that no ionic intermediates are involved in the epoxidation of alkenes. The reaction rate is not very sensitive to solvent polarity." Stereospecific syn addition is consistently observed. The oxidation is considered to be a concerted process, as represented by the TS shown below. The plane including the peroxide bond is approximately perpendicular to the plane of the developing epoxide ring, so the oxygen being transferred is in a spiro position. 

The stereochemistry of the spiro position in 112 and 113 was deduced by the comparison of their CD spectra with those of authentic yohimbine-oxindoles (81). The isomer (113) was predominantly epimerized to 112 in hot pyridine. A similar behavior was observed in two yohimbine-oxindoles, also supporting the assumption that 112 has the IS and 113 has the 7R configuration, respectively. ATa-methoxyyohimbine (111) was successfully converted into ATa-methoxyoxindole derivatives (112 and 113) in 38 and 29% yields, respectively, by treating with i-BuOCl in aqueous THF in the presence of MgO. 

The key step remaining involved the conversion of the ketone functionality in 260 to a spiro-oxindole. The conversion of a sterically hindered ketone to an oxindole by applying most of the conventional methods for the creation of a quaternary center at the spiro position was not an easy process. A process involving C—C bond formation by combination of two radical centers generated by photolysis of the alkoxy-substituted-1-alkenylbenzotriazole was then investigated (Scheme 35). By applying Wender s procedure (102), the benzotriazole derivative 261 was converted to 262 by metallation-silylation, and then the trimethylsilyl derivative was... 

Figure 5.12 The (a,b) spiro-5, (c,d) spiro-6 and (e) spiro-3,5 subunits found in 3-ring-containing silicate-based zeolites. Small circles indicate Si atoms, and large circles represent heteroatoms that have a preference to occupy a position within 3-rings Be (a-d), Zn (a,c,d), or Li (b,d) atoms. Note that Li is located at the spiro position of these building units, while Zn atoms occupy a peripheral vertex of their 3-rings. By contrast, Be has been found at central (NAB) and peripheral (LOV) positions of spiro-5 units and at central (LOV) or 3-ring peripheral (LOV, NAB and OBW) positions of spiro-6 units. In OBW and OSO, 3-rings belong to several spiro-5 units simultaneously and, thus, central and peripheral positions of spiro-5 units are indistinguishable...

In spiro compounds containing at least one fused or bridged (von Baeyer) hydrocarbon system the specifier spiro is followed, enclosed in square brackets, by the names of the components including their individual numberings. Spiro positions are again given the lowest possible locants and placed between the component names. 

To number a monospiro system, begin at an atom adjacent to the spiro position in the smallest ring and continue around that ring back to the spiro atom which takes the next available number. Then number around the... 

In the presence of a double bond at a suitable position, the CO insertion is followed by alkene insertion. In the intramolecular reaction of 552, different products, 553 and 554, are obtained by the use of diflerent catalytic spe-cies[408,409]. Pd(dba)2 in the absence of Ph,P affords 554. PdCl2(Ph3P)3 affords the spiro p-keto ester 553. The carbonylation of o-methallylbenzyl chloride (555) produced the benzoannulated enol lactone 556 by CO, alkene. and CO insertions. In addition, the cyclobutanone derivative 558 was obtained as a byproduct via the cycloaddition of the ketene intermediate 557[4I0]. Another type of intramolecular enone formation is used for the formation of the heterocyclic compounds 559[4l I]. The carbonylation of the I-iodo-1,4-diene 560 produces the cyclopentenone 561 by CO. alkene. and CO insertions[409,4l2]. 

The reaction of arylnitrile oxides with 1,1-diphenylallenes gave a mixture of 4-methylene-2-isoxazolines (Scheme 106) with major attack at the C(2)—C(3) double bond (74JCS(P2)l30l, 76CSC67, 76CSC71, 72JCS(P2)1914) and not a mixture of the 4- and 5-methylene compounds. 1-Phenoxyallene and benzonitrile oxide produced a mixture of positional isomers and a spiro compound (Scheme 107) (79JOC2796). 

An ipso attack on the fluorine carbon position of 4-fIuorophenol at -40 °C affords 4-fluoro-4-nitrocyclohexa-2 5-dienone in addtion to 2-nitrophenol The cyclodienone slowly isomenzes to the 2-nitrophenol Although ipso nitration on 4-fluorophenyl acetate furnishes the same cyclodienone the major by-product is 4 fluoro-2,6-dinitrophenol [25] Under similar conditions, 4-fluoroanisole pnmar ily yields the 2-nitro isomer and 6% of the cyclodienone The isolated 2 nitro isomer IS postulated to form by attack of the nitromum ion ipso to the fluorine with concomitant capture of the incipient carbocation by acetic acid Loss of the elements of methyl acetate follows The nitrodienone, being the keto tautomer of the nitrophenol, aromatizes to the isolated product [26] (equation 20) Intramolecular capture of the intermediate carbocation occurs in nitration of 2-(4-fluorophenoxy)-2-methyIpropanoic acid at low temperature to give the spiro products 3 3-di-methyl-8 fluoro 8 nitro-1,4 dioxaspiro[4 5]deca 6,9 dien 2 one and the 10-nitro isomer [2d] (equation 21)... 

The mechanism for the conversion of the A -oxide (94) to the o-methylaminophenylquinoxaline (96) involves an initial protonation of the A -oxide function. This enhances the electrophilic reactivity of the a-carbon atom which then effects an intramolecular electrophilic substitution at an ortho position of the anilide ring to give the spiro-lactam (98). Hydrolytic ring cleavage of (98) gives the acid (99), which undergoes ready dehydration and decarboxylation to (96), the availability of the cyclic transition state facilitating these processes. ... 

A further example of the importance of this type of stereoelectronic effect is seen in the reactions of /-butoxy radicals with spiro[2,n]alkanes (22) where it is found that hydrogens from the position a- to the cyclopropyl ring arc specifically abstracted. This can be attributed to the favorable overlap of the breaking C-H bond with the cyclopropyl cr bonds.120131 No such specificity is seen with bicyclo[n, 1,0]alkanes (23) where geometric constraints prevent overlap. 

Wehle, D. Fitjer, L. Tetrahedron Lett., 1986, 27, 5843, have succeeded in producing two conformers that are indefinitely stable in solution at room temperature. However, the other five positions of the cyclohexane ring in this case are all spiro substituted with cyclobutane rings, greatly increasing the barrier to chair-chair interconversion. 

As discussed in connection with the facial selectivities of 7-methylidenenorbom-ane 46 and bicyclo[2.2.2]octene 48, the components of the molecules, i.e., n functionality and two interacting o orbitals at the two P positions, are the same, but the connectivity of these fragments, i.e., the topology of the n systems, is different (A and B, Fig. 9). A similar situation was found in the case of spiro[cyclopentane-l,9 -fluorene] 68 [96, 97] and 11-isopropylidenedibenzo-norbomadienes 71 (see 3.4.1 and 3.4.2) [123]. In these systems, the n faces of the olefins are subject to unsymmetrization due to the difference of the interacting orbitals at the P positions. In principle, consistent facial selectivities were observed in these systems. 

The sterically unbiased dienes, 5,5-diarylcyclopentadienes 90, wherein one of the aryl groups is substituted with NO, Cl and NCCHj), were designed and synthesized by Halterman et al. [163] Diels-Alder cycloaddition with dimethyl acetylenedicarbo-xylate at reflux (81 °C) was studied syn addition (with respect to the substituted benzene) was favored in the case of the nitro group (90a, X = NO ) (syrr.anti = 68 32), whereas anti addition (with respect to the substituted benzene) is favored in the case of dimethylamino group (90b, X = N(CH3)2) (syn anti = 38 62). The facial preference is consistent with those observed in the hydride reduction of the relevant 2,2-diaryl-cyclopentanones 8 with sodium borohydride, and in dihydroxylation of 3,3-diarylcy-clopentenes 43 with osmium trioxide. In the present system, the interaction of the diene n orbital with the o bonds at the (3 positions (at the 5 position) is symmetry-forbidden. Thus, the major product results from approach of the dienophile from the face opposite the better n electron donor at the (3 positions, in a similar manner to spiro conjugation. Unsymmetrization of the diene % orbitals is inherent in 90, and this is consistent with the observed facial selectivities (91 for 90a 92 for 90b). 

The regiochemical course reacting saturated ketones depended on the substitution pattern of the a-positions. In most cases, the intermediate oxime had an anti N-OH function with respect to the chain branched a-position. Consequently, the more substituted alkyl group preferentially migrates. This advantage was utilized for synthesizing the spiro a-amino-e-caprolactam (202 203, Scheme 38) [12c], the Mexican bean beetle azamacrolide allomone (205 206, Scheme 39) [44 a], in a key step of the chiral synthesis of benzomorphanes... 

Instead of metal chelation, an intramolecular hydrogen bonding between the oxygen atom of phenolate and a hydrogen atom of a carboxylic acid in the 8-position leads to stabilization of the colored form, such as compound 12.20,21 This spiropyran exhibits reversed photochromism, which means that thermally stable species change from the spiro form to the colored form, and thus the colorless form produced by photoirradiation soon converts to thermally stable colored form. 

The colored form of spironaphthopyran 32 absorbs at A,max of ca. 450 m,70 and the closed spiro form is colorless, which has no absorption band above 400nm. Bulky substituent group is especially important for photochromic sunglass. Introduction of the spiroadamantane or spirobi-cyclo[3.3.1]heptane into the 2-position of naphthopyran increases the resistance to photo-fatigue reaction, since endocyclic double bond induced by 1,7-hydrogen shift in the colored form cannot be formed in 2-adamantyl or 2-bicycloheptanyl group. 

Another approach to shift absorption bands for the colored form is the extension of Jt-conjugation outside the spiro skeleton. Procedures of molecular designs for such photochromic compounds are shown in Scheme 20. (1) Position for extension of additional -conjugation in spirothiopyran... 

Fluoran (1) is the commonly used name for the spiro [isobenzofuran- 1,9 -xanthen]-3-one. Benzo[a]fluoran (2) has the benzene ring fused to the 1-and 2-positions of the xanthene moiety. Fusion at the 3- and 4-positions gives benzo[c]fluoran (3). Numbering of the atoms is employed as shown in 1-3. 

Fluoran compounds have an optically active spiro-carbon atom. Consequently, some fluoran compounds, especially those having an alkylamino group of four or more carbon atoms at 3 -position, have been found to exhibit crystal modifications as determined by X-ray diffraction. Each crystal modification reveals different physical properties such as melting point, solubility, and affinity with acidic compounds, resulting in different characteristics regarding use for carbonless copying papers, thermosensitive recording papers, and the like. 

Chapter 4 is concerned with a technically important group of leuco compounds which like the spiropyrans are not formed by reduction of the parent dye, but by formation of a spiro structure from the dye in such a way that the newly created sp3 center destroys the conjugation, and hence, the color of the chromophore. These are the phthalides (spirolactones) and the position of equilibrium is determined by pH rather than a redox process. Such materials are used mainly as color formers in pressure-sensitive... 

When the indole 3-position is already substituted, electrophilic reagents attack the 2-position instead often through a 3,3-spiro intermediate. For example, when 2-(3-indolyl)ethylmercaptan (27) reacts with methyl acetoacetate, the thia-p-carboline analogue 31 results. It seems plausible that the reaction involves initial hemithioketal formation (28), followed by electron release by the indole nitrogen and hydroxide... 

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