Benzo spiro rings

Figure 7 Ligands with benzo spiro ring and spiro[4.4]nona- 1,6-diene backbones...

Ohwada extends his theory, unsymmetrization of n orbitals, to Orbital Phase Environment including the secondary orbital interaction (Chapter Orbital Phase Environments and Stereoselectivities by Ohwada in this volume). The reactions between the cyclopentadienes bearing spiro conjugation with benzofluorene systems with maleic anhydride exemplified the importance of the phase environment. The reactions proceed avoiding the out-of-phase interaction between dienophile LUMO and the HOMO at the aromatic rings. The diene 34 with benzo[b]fluorene favored syn addition with respect to the naphtalene ring, whereas the diene 35 with benzo[c]fluorene showed the reverse anti preference (Scheme 22) [28]. 

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. 

In contrast, radical polymerization of 2,3-benzo-7-methylene-l,4,6,9-tetraoxa-spiro[4.4]nona-2-ene (138) gave only a vinyl polymer (139) with no occurrence of ring-opening isomerization, even in the solution polymerization at 165 °C. [105] It appears that the propagating radical having a spiro orthocarbonate structure is too stable to liberate the corresponding carbonyl compound, phenylene carbonate. 

When A.A-dimethylisoindolinium bromide is treated with phenyl-lithium, it gives V-methylisoindole via the ylid (54).2 59,60 An attempt to prepare benzo[c]thiophene via the analogous ylid (55) failed. Thus, when l,3-dihydrobenzo[c]thiophene methylsulfonium iodide was treated with phenyllithium, it gave a mixture of methyl phenyl sulfide, spiro[5.5]-l-methylthio-2,3-benzo-6-methylthio-methyleneundeca-7,9-diene (56), and 3,4-bis(methylthio)-l,2 5,6-dibenzo-l,5-cyclooctadiene (57).59,60 The formation of methyl phenyl sulfide may be explained by the formation and ring cleavage of compound 58, and compounds 56 and 57 arise by Diels-Alder dimerization of the o-quinodimethane (59) formed by ring cleavage of the ylid (55). 

Several saturated parent systems shown in Scheme 1, especially (2), (4) and (7), have been incorporated into spiro compounds or have been fused with a variety of non-aromatic carbocyclic or heterocyclic rings. Unsaturated compounds with an endocyclic carbon-carbon double bond, formally possible in all systems with three adjacent heteroatoms, are only known in very few cases (e.g. cyclic sulfites and sulfates of enediols) or in the form of benzo or other condensed systems (mainly cyclic sulfites and sulfates of aromatic 1,2-dihydroxy compounds). For details concerning the various types of derivatives, see Section 4.33.4.2. 

In an analogous manner, treatment of 4-(2-haloethyl)-phenols and -l-naphthols " with bases produces spiro[2.5]octa-4,7-dien-6-ones and their benzo analogues, respectively. The basic treatments of jS-oxiranyl ketones , esters (equation 13) , nitriles , sulfones and alkynes affords 2-(hydroxymethyl) cyclopropyl derivatives, usually as the sole cyclization product. The cyclization occurs regiospecifically by the intramolecular attack of the anion on the y-carbon in the oxirane ring. Attack of the anion on the 5-carbon in the oxirane, which should lead to the formation of cyclobutanols, usually does not take... 

Fig. 18.10 Molecular variations applied to diazepam (1). Compounds (2) and (3) are positional isomers optical isomerism is introduced in (4). Compound (5) is a vinylogue (vinylogy is also used to render amidic the carbonyl of (14). Compounds (6) and (7) are isosteres. Compounds (8) to (15) result from various ring modifications enlargement (8), contraction (9), introduction of additional rings (10 and 11), benzo splitting (12), use of spiro systems (13 and 14), ring opening (15). Compound (16) is a symmetrical twin drug and compound (17) underlines that many substituent variations can be used. The presented structures do not strictly correspond to existing molecules.

A variety of spiro-linked 4//-l,3-benzodithiins have been obtained from the reaction of 2//-benzo[(t]thiete with compounds containing a C=S unit. The four-membered ring acts as a source of a thioquinone methide <97LA1603>. 

Because (2) has a plane of symmetry through C-5 and S-1, there are only five possible mono-substituted derivatives, neglecting conformational isomers whereas (1) has no such plane of symmetry and all eight possible monosubstituted derivatives are possible. In addition to conformational isomers (axial-equatorial or cis-trans), there is one nonconjugated tautomer of (1), the 47/-thiocin (4). There are no reports of ring (4) except for benzo-fused thiocins and a reported spiro compound (see Section 9.20.3.3). For tetrahydro derivatives, particularly 2i/-3,4,7,8-tetrahydrothiocin (5) for example, there is the possibility of cis-trans isomerizations of the double bond. 

Corey and Boger have explored the enormous synthetic potential that benzo-thiazoles have to offer as carbonyl equivalents, and have successfully applied their results to the development of novel procedures for generating fused and spiro five- and six-membered rings ° as summarized in Scheme 19. In a subsequent... 

N-phenylmaleimide. The formation of 2-phenacylidene-3-methyl-5-phenyl-l,3-oxazoline by the treatment of the salt (158) with sodium hydride in DMSO was considered to proceed through the thiocarbonyl ylide (159). However, the thiocarbonyl ylide (160), which in a similar manner to that mentioned above was generated from its corresponding dithiolanium salt, instead underwent a spontaneous ring-closure, yielding the spiro-compound (161). The thiocarbonyl ylide dipolar characteristics of phenyl-substituted thieno[3,4-c]pyrroles, phenyl-substituted thieno[3,4-c]thiophens, and the thieno[3,4-/)benzo[c]thiophen (162) have been substantiated by their reactions with dipolarophiles. The first representative (164) of the hitherto... 

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