Highly substituted aromatic

Entry 6 uses diisopropoxytitanium with racemic BINOL as the catalyst. Entry 7 shows the use of (CH3)2A1C1 with a highly substituted aromatic aldehyde. The product... 

Application of l,n-ADEQUATE for highly substituted aromatic compounds... 

Scheme 1 Synthetic route for the preparation of a highly substituted aromatic intermediate in the synthesis of euglobal-G2 [30]. The two possible product structures are shown with key long-range couplings. Based on the INADEQUATE data, 33 was the sole product of the reaction.

At temperatures above 450°C ZSM-5 is a very effective catalyst for the disproportionation of toluene. A process has been developed and put into commercial practice (2). The thermodynamic equilibrium composition (11) is listed in Figure 7. The product obtained with ZSM-5 contains less of the highly substituted aromatics, as a result of diffusion and transition-state inhibition, such that the process can be approximated by the equation ... 

The general process is one of loss of nitrous acid from the adduct (4) in highly substituted aromatics the initially formed adduct may well also rearrange either by hydroxyl or other group migration. 

The four Problems are arranged in increasing order of difficulty. They involve several common functional groups, a highly substituted aromatic ring, a substituted heteroatom ring with a chiral center, and a diunsatur-ated terpenol. Extensive use is made of 2-D spectra. 

This [2+2 + 2]cycloaddition is useful for synthesis of highly substituted aromatic compounds since substitution reactions with arenes are seldom regiospecific. An example is the synthesis of calomelanolactone (2) from triyne l.5... 

The present overview deals with the application of Fischer chromium carbene complexes in the benzannulation reaction for the preparation of highly substituted aromatic compounds. Before focussing on specific arenes (Section 8.5), details of the mechanism are given (Section 8.2), and the scope and limitations of the reaction are defined (Section 8.3). A short description of the experimental procedure is given thereafter (Section 8.4). Finally, the contribution deals with the application of the chromium carbene benzannulation to natural compounds and molecules with biological activity (Section 8.6). 

Sterically congested thiophene 1,1-dioxides are less prone to dimerization the most stable is the tetrachlorothio-phene 1,1-dioxide. Other congested thiophenedioxides such as 3,4-di-/-butyl, 3,4-diadamantyl, and 3,4-dineo-pentylthiophene 1,1-dioxide undergo [4-1-2] cycloaddition with electrophilic dienophiles followed by SO2 extrusion to produce highly substituted aromatic compounds (Scheme 30) <1998JOC4912>. 

The Birch reduction of aromatic hydrocarbons and ethers to the 2,5-dihydro derivatives proceeds most satisfactorily when the substitution pattern allows the addition of hydrogen to two unsubstituted positions in a para relationship. If this requirement is satisfied, better yields are obtained from more highly substituted aromatic rings than from (say) anisole itself, which affords a substantial amount (20%) of 1-methoxycyclohexene (c/. Scheme 1). Extra substitution presumably hinders protonation at the terminus of the dienyl anion (which would lead to a conjugated diene and overreduction). The utilization of anisole moieties as precursors to cyclohexenones has been of very limited value with many 1,2,3-substitution patterns and more densely substituted derivatives. Compounds (23) to (26), for example, have only been reduced by employing massive excesses (200-600 equiv.) of lithium metal,2 while the aromatic ring in (28) is completely resistant to reduction. ... 

There are no trichloro- or tetrachlorobenzenes to compare with 2,3,5-trichloro-or 2,3,5,6-tetrachlorobenzene-l,4-diol. Neither are there any completely satisfactory isodesmic reactions for which there are the necessary data to disentangle the myriad steric and electronic effects in these highly substituted aromatic rings. 

An analogous vinylketene intermediate (127, see Schemes 57 and 59) as proposed for the Dotz reaction has been assumed in the so-called cyclobutenedione methodology [161]. The key intermediate is a 4-aryl or 4-alkenyl substituted 2-cyclobutenone (128) that can be obtained e.g. by the reaction of the 3-cyclo-butene-1,2-dione (129) with the appropriate lithium reagent or Stille coupling with 4-chloro-3-cyclobutenone. Thermal cyclobutenone ring opening to the vinylketene 130 followed by electrocyclization furnishes the highly substituted aromatic compound 131 (see Scheme 59). 

A method for the synthesis of highly substituted aromatic and heteroaromatic hydroxy compounds is the photochemical Wolff rearrangement of an unsaturated a-diazo ketone in the presence of an alkyne. The product, an alkenylcyclobutenone, undergoes ringopening and recyclization to a phenol (equation 60). Three examples of the reaction are the formation of the naphthols 587 and 588 and that of the hydroxybenzofuran 589. Complexes 590 (R = alkyl or aryl r-alkyl or Me3Si), produced from THF, alkynes and... 

In independent research Danheiser and coworkers applied the reaction of siloxyalkynes with cyclobutenones to the synthesis of various highly substituted aromatic compounds 47 (equation 31). 

Danheiser and coworkers have developed a convenient synthetic approach to useful, highly substituted, aromatic compounds by the reaction of alkoxyacetylenes with cyclobutenone derivatives (equation 61) . The mechanism of this annulation is similar to the analogous reaction of siloxyacetylenes (equation 31, Section II.D.2) and the key step is a [2+2] cycloaddition of alkoxyacetylene with a vinylketene intermediate. ... 

At the temperature of maximum fluidity the vibration at 860 cm reaches Its maximum. This peak, which arises from highly substituted aromatic rings. Is consistent with a model of liquid crystals composed of layered aromatic sheets with lone hydrogen atoms only on the edges. The 860 cm peak becomes significant In each coal at only one temperature. In another Pittsburgh No. 8 samplj, whose fluidity was severely reduced by oxidation, the 860 cm peak did not become significant at any temperature. Hence, fluidity and mesophase are evidently related. 

The steric limitations for this rearrangement are illustrated by the spectra of the two highly substituted aromatic compounds that follow. With one ortho methyl group, the rearrangement proceeds to give a peak at mk 120, but if both ortho positions are substituted, the reaction is blocked (Equation 2.64). 

More highly substituted aromatics have also been studied in the course of natural product synthesis. For example, rhodium(II) mandelate-catalyzed cyclization of diazoketone 41 produces the ring expanded product 42, which on hydrogenations furnishes the tricyclic lactone 43. ... 

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