Bis-annulation

A number of other ring systems have been prepared by intramolecular bis-annulation procedures. Pyrrolothiadiazolines 174 were prepared by condensation between hydrazides and compound 173 (Equation 14) <1998JPR676>. The thermally induced intra-intermolecular criss-cross cycloaddition of azine 175 in the presence of phenyl isocyanate leads to heterocyclic compound 176 containing three fused five-membered rings (Equation 15) <2002TL6431>. 

Exposure ofpara-qmnonc diimine and allylsilane to ZnCl2 in dichloromethane leads to a slow bis-annulation reaction to give the pyrroloindole derivative in which the two silyl groups are traits to each other <20020L953>. The results of optimization studies revealed that the amount and nature of the Lewis acid used and the temperature employed play an important role in determining the course of the reaction (Equation 90). 

N. Naz, T. H. Al-Tel, Y. Al-Abed, and W. Voelter, Synthesis of polyfunctionalized bis-annulated pyranosides Useful intermediates for triquinane synthesis, Tetrahedron Lett. 35 8581 (1994). 

R. Tsang and B. Fraser-Reid, Pyranose ct-enones provide ready access to functionalized trans-decalins via bis annulated pyranosides obtained by intramolecular Diels-Alder reactions a key intermediate for forskolin, J. Org. Chem. 57 1065 (1992). 

A. A. Ghini, C. Bumouf, J. C. Lopez, A. Olesker, and G. Lukacs, Intramolecular Diels-Alder reactions on pyranose trienes. Stereoselective access to bis-annulated pyranosides. Tetrahedron Lett. 37 2301 (1990). 

R. Tsang and B. Fraser-Reid, Serial radical cyclization via a vinyl group immobilized by a pyranoside. A route to bis-annulated pyranosides, J. Am Chem Soc. 108 2116 (1986). 

This family is not a particularly populous one. At present, it appears to consist of just two fundamentally different members. The first of these, the bis-annulated 12 - disulfide (53), was prepared by ring-forming condensation of dialdehyde (47) with bis Wittig reagent (45b).58 It is a colorless substance characterized by unexceptional 1H NMR absorptions. For obvious reasons, the heavily buckled atropic nature of 53 may readily be rationalized in terms of the exact same factors advanced to explain the behavior of the triheteronins. 

Bis-annulated-triazine-pyridine (BATP) CyMe4-BTP Bis-annulated-triazine-pyridine (BATP) < >CyMe4-BTP... 

The l,3,4-thiadiazolo[ ]-fused system can be conveniently prepared by intramolecular bis-annulation procedures for example, pyrrolothiadiazolines 90 are prepared by condensation between hydrazides and compound 89 (Scheme 53) <1998JPR676>. 

Halterman and Vollhardt and Paquette and coworkers have prepared bis(annulated cyclopentadienyl)titanium complexes, and have separated (25) and (26) when starting from the chiral natural product camphor. They have shown that... 

Only a few cases of thermal electrocyclizations of [1,2 3,4] bis-annulated trienes have been described. That die central double bond is part of a ring system eliminates the possibility of secondary thermal processes that were operating in the precursors to the simpler type IV cyclohexadienes. For example, the cyclization of diketone (239) to (240) takes place smoothly without interference from other thermal processes. ... 

Carbanions of a-haloalkyl aryl sulfones, sulfonates and sulfonamides react with quinoxalines according to two general pathways vicarious nucleophilic substitution of hydrogen and/or bis-annulation to bis(azirino)quinoxaline derivatives. The charge distribution in the anionic (T-adducts and reaction conditions influence the direction of these reactions. ... 

A bis-annulated carbohydrate has been reported by Pipelier and Ermolenko [368] in their synthetic route to quadrone. This complex stmcture was elaborated from levoglucosan by two successive branchings of allyl groups at C2 and C4 using epoxide opening methodology. A keto group, formed from the alcohol at C3, allowed initial cyclopentenone constmction. Further manipulation of this ketone allowed a second Robinson annulation to form the second fused six-membered carbocycle. 

Using a y-hydroxyalkynoate combines two effects - the unusual contra-electronic regioselectivity leading to a-attack and a cyclization evolving from the juxtaposition of the hydroxyl and ester functionalities. Thus, as shown in Equation 1.41, the initial adduct 35 between hydroxyalkynoate 33 and alkene 34 spontaneously lactonizes upon its formation to form butenolide 36. The presence of a second monosubstituted double bond proceeds equally facilely in like fashion such that the bis-annulated product 37 is directly formed [38]. Chemoselective addition of the less sterically... 

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