Annulization, linear

Annulated linearly fused cycloheptadienes 6 are prepared by intramolecular cyclopropanation of dienic esters with a,) -unsaturated diazo compounds, followed by in situ rhodium-catalyzed rearrangement. ... 

A double linear annulation was observed in the benzannulation reaction of the helical biscarbene complex 27 with 3-hexyne along with a product bearing... 

Johnson has developed two linear approaches to synthesize the C-nor-D-homosteroid skeleton (Scheme 2.2). In his first approach [21], tetralone 19, obtained from reduction of 2,5-dimethoxynaphthalene, was used as the source of the C,D-rings. The B- and A-rings were constructed by sequential Robinson annulations (19 —> 20 —> 21). The Cl 1,12 olefin was then introduced to provide 22. Ozonolysis of 22 followed by an aldol reaction of the resulting dialdehyde gave 23. Subsequent deformylation and deoxygenation afforded the cyclopamine skeleton 24. 

Interestingly the heteroallyl anion 26 from antipyrine displayed unusual 1,2-mode Type 1 (la) reactivity with 6.40 instead of Type III (3a) reactivity as generally observed in the preceding examples. The carbinol acetal 76 thus formed by 1,2-addition mode was cyclized with BF3.Et20 to afford the corresponding linearly annulated carbazole 77 in 73% yield <99T11563>. 

This wide range of transformations includes many reactions which are one way or another connected with cyclopropane derivatives. The cyclopropane moieties can be part of the structure of both the linear dienes or of annulated polycyclic unsaturated systems as well as being part of a spiro compound. 

Reaction of linear conjugated dienes with la at —10 °C in hydrocarbon solvent in the presence of McsSiCl/AlCls affords stereospecific tra i-l-silyl-3-vinyl-cyclopentanes, indicating a [3 + 2] cycloaddition of the allyl group of la with a carbon arbon double bond of the diene [Eq. (9)]. In the [3 + 2] annulation reaction, of greater significance is the tram conformation of the trimethylsilyl group and vinyl groups. 

Vol. 5, p. 76). Related studies have shown that the butenolide derivative (319) can be used as an annulating agent in the construction of linear tricyclic y-lactones [cf. (322) and (323)] and it is expected that this methodology may be applied to the synthesis of naturally occurring eudesmanolides." ... 

Linear annulated dioxins synthesis were reported by analogy with that of the 1,4-benzodioxin series <2002T1533> or in a modification of the Ullmann ether synthesis <2004T8899>. 

Synthesis of pyrido[ 1,2-bJquinazolines through formation of the azole ring from properly substituted quinazoline precursors is also known (61AP556). Thus, the cyclodehydrobromination of the 2-(4-bromo-butyl)quinazolin-4-one (445) with alkali was claimed to give only the linearly annulated 1,2,3,4-tetrahydropyrido[ 1,2-6]quinazolin-4-ones (446) (61AP556). Oxidation of the 3-amino-2-(butyn-l-yl)quinazolin-4-ones (447) with lead tetraacetate led to intramolecular addition of the produced /V-nitrene intermediate to the triple bond to give 449 [86JC S(P 1) 1215]. 

Anti-tumor compound (205)-irinotecan (1) was prepared in 13 steps with an overall yield of 1.15 % for the longest linear synthesis. The short and selective preparation of aryl iodide 11 features two key steps - ortho metalation and Sharpless asymmetric dihydroxylation. In only one step 11 is transformed into the target molecule 1 by application of a radical domino annulation with isonitrile 15. This method gives access to the broad family of campthotecin derivatives because of the quite impressive generality of the substrates that can be employed. 

The electronic absorption spectra of PAHs have attracted great attention whereby different approaches toward classification of the particular bands have been proposed.142 A generally valid approach191 identifies (i) a-bands (Lb in the Platt nomenclature192) which relate to the longest wavelength absorption of benzene and are relatively weak and possess a distinct vibrational structure, (ii) p-bands (La) of medium intensity and are more sensitive to a linear annulation than the a-bands, and (iii) /1-bands (Ba, Bb) which are intense and have no vibrational structure. 

Figure 9. Solid-state UV—vis spectra of homologous series of PBAHs with linear annulation (Dm, symmetry).

The benzannulation of naphthyl carbene complexes may be used as a direct route to functionalized phenanthrenes (Scheme 34) [37a]. While it is obvious that 1-naphthyl carbene complexes such as 87 lead to phenanthrenes 88 (see also Section 8.3.2, Scheme 19), chromium 2-naphthylcarbenes 89 offer two alternatives for annulation, giving either phenan-threne or anthracene derivatives. Generally, angular benzannulation affording phenanthrenes 90 is favored over linear benzannulation to give anthracene derivatives 91. A rationale for this regiopreference is the higher electron density at C-l compared with that at... 

To date, reports of linear benzannulation are very limited [55b, 79]. One example referred to the annulation of a 2-naphthohydroquinoid chromium carbene, which was employed in the synthesis of anthracycline (see Section 8.6.2) [79]. Later, a complementary approach in this area started from 2-naphthylcyclopropenes which, in the presence of hexacarbonyl-molybdenum, served as precursors for the vinyl ketenes required for linear annulation [55b],... 

Other influences, however, also play a part, thus the absorption band of the acenes with linear annulization is at a longer wave length than that of the corresponding phenes with angular annulization (comp, anthracene 3800 A with phenan-threne 3400 A naphthacene 4750 A with 1,2-benzanthracene 3850 A, 3,4-benzphenanthrene 3650 A, chrysene 3600 A, triphenylene 3500 A). 

However, reaction of MVK with linear dienamine 5244 and with the cross-conjugated dienamine 5445 gave only the corresponding oc,/ -annulation products 53 and 55, respectively (Scheme 29). 

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