Indanes, ring systems

In particular, the key intermediate product 381 in the synthesis of wighteone was prepared by the oxidative rearrangement of 3 -iodotetraalkoxychalcone 380 [474] and the key step in the synthesis of ( )-indatraline involved the HTIB-promoted diastereoselective ring contraction of a 1,2-dihydronaphthalene 382 to construct the indane ring system 383 (Scheme 3.152) [475]. A similar oxidative rearrangement of 3-cinnamoyl-4-hydroxy-6-methyl-2/7-pyran-2-ones with HTIB in dichloromethane followed by cycliza-tion was used by Prakash and coworkers for the direct conversion of o-hydroxychalcones into isoflavone derivatives [476]. 

Indane as a Building Block for Three-Dimensional Ring Systems. . 169... 

On the other hand, in the synthesis of cholesterol (30) by Woodward and CO workers [10] the less stable fran -configuration between rings C and D is attained through a homosteroid (29). i.e. a steroid analogue in which the C/D indane system is substituted by a decalin in which the rran -configuration is the thermodynamically favoured (Scheme 8.7). The conversion of the six-membered ring into one of five members is carried out at a later stage, under conditions that do not affect the preformed tran -junction. 

The ease of cyclobutane cleavage and the detailed mechanism can be affected by the nature of the substituents and the substitution pattern. While the above cyclobutanes are cleaved without a discernible intermediate, the n//-head-to-head dimer of dimethylindene shows a significantly different behavior. This substrate is cleaved in an apparent two-step process, involving a ring-closed radical cation (with spin and charge localized on one indan system) and a ring-opened 1,4-bifunctional radical cation. Apparently, the cleavage of the doubly benzylic cyclobutane bond is reversible. The involvement of more than one dimer radical cation is indicated by a unique polarization pattern (Fig. 13), which is incompatible with any one intermediate, but can be simulated on the basis of two successive radical cations (see Sect. 5.2) [256]. 

Cava, M. P., LItle, R. L., Napier, D. R. Condensed cyclobutane aromatic systems. V. The synthesis of some a-dlazoindanones ring contraction In the Indan series. J. Am. Chem. Soc. 1958, 80, 2257-2263. 

This review comprises the advances in fusing benzene and other arene rings to three-dimensional cores which consist of multiply fused cyclopentane rings. Indane represents the parent building block here, and polycyclic frameworks consisting of several indane units fused in three dimensions have been called the centropolyindanes [28,29]. As will be shown in this chapter, centropolyindanes comprise some other well-known sub-classes of polycyclic hydrocarbons treated in comprehensive reviews, viz. propellanes [30,31], triquinacenes [32,33], and fenestranes [34-37] as well as even more exotic polycyclic systems of unusual topology [38]. 

---