1.3- Disubstitution pattern

The latter were assumed to have the 1,3-disubstitution pattern. Both sets of compounds proved to be considerably more air and thermally sensitive than the parent system. Whereas irradiation in sealed tubes did not result in any observable change, simple heating produced insoluble clusters ( 3). In an effort to suppress bimolecular reactions two of the complexes [R = C6H5(CH2)35 C6H5CHCH3(CH2)2] were subjected to flash vacuum pyrolysis at low contact times (300-950°C, 2xl0-l+torr) (57 ). The resulting... 

For substituted tricyclo[4.1.0.02,7]heptanes, similar addition of benzenethiol in diethyl ether gave an isomeric mixture of bicyclo[3.1.1]heptanes.35 As shown in the mechanistic scheme, the 1,3-disubstituted patterns of the bicyclo[3.1, l]heptanes are governed by the regiospecific attack of the thiol radical on the sterieally less hindered bridgehead carbon. The results of these radical additions arc summarized for bicyclo[n.l.l]alkanes (Table 8)35 and bicyclo[1.1.0]butanes (Table 9). 

We already mentioned that among the disubstituted Fc derivatives, the 1,3-disubstitution pattern is the one that induces the highest mesomorphic tendency, but because of the bulkiness of Fc, four rings are required for mesomorphism to occur. This observation confirms that Fc tends to decrease the liquid-crystalline tendency of the materials onto which it is included. 

We need to look at the proton expansions provided in the problem to confirm the assignments made for the aromatic protons. The Hertz values shown on the expansions allow us the opportuniU to obtain coupling constants that confirms the 1,3-disubstitution pattern. The splittings observed in the expansions can be explained by looking at the coupling constants, V, and V, present in the compound. couplings are either zero or too small to be observed in the expansions. 

The origin of planar chirality is depicted in Fig. 1. For ACTCs, complexes displaying an unsymmetrical 1,2- or 1,3-disubstitution pattern (or related unsym-metrical higher substitution) are no longer superimposable with their mirror images (A vs ent-A). In case that the respective side chains are capable of exercising as donor moieties for chelation or coordination to transition metals, optically active complexes B result that have potential as asymmetric metal catalysts or catalyst precursors [9,10]. 

It has been mentioned already that among the disubstituted ferrocene derivatives, the 1,3-disubstitution pattern induces the highest mesomorphic tendency. The fact that (295) and... 

A flaw m Kekule s structure for benzene was soon discovered Kekule s structure requires that 1 2 and 1 6 disubstitution patterns create different compounds (isomers)... 

Vicinal (Section 8.2) A term used to refer to a 1,2-disubstitution pattern. For example, 1,2-dibromoethane is a vicinal dibromide. 

The 2,6-disubstitution pattern of a pyridine can also be found in (formally) 4-hydroxy-substituted pyridinocrowns [19] or [20] (Nakatsuji et al., 1985 Vogtle et al., 1991). Basicity measurements have also been carried... 

This intermediate has the oxygenation and pattern and frans-disubstitution pattern found in the prostaglandins. Several syntheses of similar intermediates have been developed.239... 

Alkenes with a 1,1-disubstitution pattern form tertiary carbocations upon treatment with a Brpnsted acid. Consequently, such compounds are often easily reduced (Eq. 72). An example of this is the formation of 2-methylpentane in 93% yield after only 5 minutes when a dichloromethane solution of 2-methyl-1-pentene and 1.4 equivalents of triethylsilane is treated with 1.4 equivalents of trifluoromethanesulfonic acid at —75°.216 Similar treatment of 2,3-dimethyl-l-butene gives a 96% yield of 2,3-dimethylbutane.216... 

The synthesis of 2,7-dinitrodibenzothiophene via cyclization of the biphenyl derivative (38) with bromine, at 200°, could be usefully extended to the synthesis of other deactivated dibenzothiophenes. The 2,7-disubstitution pattern is rare, the only other reference to it being the... 

Nearly 35 different anthocyanins have been reported to occur in one or more species in the family Ranunculaceae (Figure 10.15), and 24 of these have been reported after 1992 as novel compounds. Flowers of species in the genera Delphinium (blue), ° Consolida (blue-violet), and Aconitum (purplish-blue) " contain similar anthocyanins with polyacyl substitution based on -hydroxybenzoylglucose residues at the 7-hydroxyl of delphinidin, in addition to a more simple glycosyl moiety at the 3-position. Red flowers of Delphinium hybridum share a similar 3,7-disubstitution pattern based on pelargonidin instead of delphinidin. 

Reactions of alkynyliodonium salts with multidentate nucleophiles can be employed for the synthesis of heterocyclic compounds. Recent examples include preparations of thiazoles, selenazoles, and 2-mercaptothiazoles by the treatment of alkynyliodonium mesylates or tosylates with thioamides, selenoamides, and ammonium dithiocarbamate (Scheme 62) [169-171]. A novel hetero-Claisen rearrangement of tricovalent iodine(III) intermediates was proposed to account for the 2,4-disubstitution pattern of the thiazoles [169]. 

From the commercial point of view, only the 2,5-diarylamino-l,4-benzoquinones have been of any significance. They were used as vat dyes for wool and cotton, but are no longer in commercial production. Other examples of early dyes of this type are listed in the Colour Index under numbers 56000-56050. The inadequate color properties of the amino-substituted benzoquinone chromogen are exemplified by 2,5-bis(dimethylamino)-l,4-benzoquinone [1521-02-4], which absorbs at 530 nm in ethanol with an absorption coefficient of only ca. 500 Lmol em1. This low intensity is characteristic of the 2,5-disubstitution pattern. Although other substitution patterns have higher intensities (e g., the 2-amino derivatives have an of ca. 5000 L mol-1 cm ), dyes based on these have not been... 

Type I ligands have a pyridine ring as the central unit, which carries two branched aliphatic sidearms, resulting in a 2,6-disubstitution pattern. The sidearms are C3 units whose central carbon atom -i.e., C-2 - is connected to the pyridine ring. The donor atoms are appended in the 1 and 3 positions, respectively. Suitable donors are N, O, S, or P (1-4). 

A surprising feature of these reactions is their apparent departure from the Michael-addition/o -elimination sequence, which is expected to lead, via alkylidenecarbenes 275, to a 2,5-disubstitution pattern in the products. This has been attributed to the initial formation of iodine(III)-sulfur(selenium) adducts 276 and their collapse by a hetero-Claisen rearrangement to the isomeric alkylidenecarbenes 277 (Scheme 78). In view... 

Among the methodological studies [9d, 9e, 20d], the rich chemistry of carbinolamine alk-oxide DMGs 59-63 (Scheme 22) [39], while not explored with regard to the scope of electrophile introduction, predicts access to highly functionalized systems. Similarly as yet unexplored but of foreseeable value for 3,5-disubstituted patterns is the use of the O-carbamate DMG, 64 —> 65 (Scheme 23) [40]. Thus, in a prototype sequence, metalation-electrophile... 

The process was simple and accommodated a wide range of substrates. Indeed, the initial paper32 reported successful application to allylic alcohols containing five of the six possible mono- and disubstitution patterns. Removal of the hydroxy group to a homoallylic position reduced the enantioselectivity below useful levels (<50%). 

Consistent with this picture, reaction of pure metallacycles with the 2,4-disubstitution pattern with nitriles gives isomerically pure 2,4,6-trisubstituted pyridines Y. Wakatsuki and H. Yamazaki, 7. Chem. Soc., Dalton Trans., 1978, 1278. 

Extensive examinations of the circular dichroism curves of pyrrolizidine alkaloids have been carried out by Culvenor et a/. and Hrbek et The free bases tested were divided into four groups, all possessing 8a-hydrogen atoms. Saturated 1-substituted pyrrolizidines [e.g., 1-methylpyrrolizidine (7) and isoretronecanol (22)] showed negative Cotton effects while with 1,7-disubstituted pyrrolizidines [e.g., platynecine (43)], the Cotton effects were positive. Dehydropyrrolizidines with 1-substituents [e.g., supinidine (96)] displayed positive Cotton effects, and those with 1,7-disubstitution patterns [e.g., retronecine (127) and heliotridine (109)] exhibited large positive... 

Halogen-lithium exchange followed by intramolecular substitution creates a new ring. Such a method is the basis of a benzodihydrofuran synthesis. The presence of two exchangeable halogen atoms (2,6-disubstitution pattern) makes it possible to introduce another functionality at C-7. ... 

Alkoxy-3-pyrrolines. Fischer carbene complexes and aldimines undergo cycloaddition in the presence of GaCl,. The major products have a tran.s-2,5-disubstitution pattern (trans cis ratio in the 8 2 range). 

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