Bridged Bi- and Polycycles

When considering the synthesis of anellated bi- and polycycles, the rapid increase in complexity associated with bicyclization reactions suggests that an evaluation of this possibility should be considered first. Therefore, determine whether the target contains a centrally located six-membered ring that can be constructed using an intramolecular Diels-Alder cycloaddition. 

In order to initiate the discussion, several skeletal bonds of 43 have been arbitrarily picked in Seheme 6.34. We would like to know which of these cuts results in the greatest retrosynthetie simplification of the target. 

The possibilities of using two-bond disconnections (i.e., the Diels-Alder transform) are easy to appreciate with respect to patchouli alcohol (50), a bridged tricyclic target. It is a historically amusing compound, as its initial (wrong) structure was proven by synthesis [163] (a proof that later had to be revised) [164] The correct structure of 50 possesses three 

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When phosphaalkynes are exposed to bis- and tris(diazo) compounds, bis- or tris(l,2,4-diazaphosphol-5-yl) compounds are formed that may be further converted into a variety of novel heterocyclic systems. For example, bis- and tris[diazo(tri-methylsilyl)methyl]phosphanes 237 and 240 afforded bis- and tris(diazaphospho-lyl)phosphanes 238 and 241 after cycloaddition with terf-butylphosphaacetylene followed by a subsequent 1,5-silyl shift (Scheme 8.56) (300). Reaction with electrophilic halides at the Wsilyl functions allows the introduction of a heteroatom bridge between the diazaphosphole ring leading to polycyclic ring systems such as 239 and 242. 

Cyclobutanediones, once exotic compounds represented by a few perhalo derivatives, have become readily available as a result of new synthetic developments in recent years. These include the modified acyloin condensation 52) in which the intermediate enediolate is trapped as bis-trimethylsilyl ether (28) which can be converted to cyclobutanedione by reaction with bromine or hydrolyzed to acyloin and oxidized in a separate step. In addition to this efficient and general method, bi- or polycyclic unsaturated cyclobutanediones (30) have become available from photolysis of bridged cyclohexenediones (29) to be discussed in the following section. Photocycloaddition of dichlorovinylene carbonate (DCVC) to olefins53) promises to provide a third route if the problems associated with hydrolysis of the photoadducts (31) can be overcome. 

Magnesium reacts with naphthalene and higher polycyclic aromatics in liquid aimnonia or HMPA to form the radical ion. Adducts with anthracene and substituted anthracenes form in THF. Depending upon substitution and conditions, they have a variety of structures. The l,10-bis(trimethylsilyl) compound had structure (47) in the crystal, with magnesium bridging the 1,10-positions (C-Mg =... 

More than 40 cyclic polysulfanes have been investigated by X-ray diffraction on single crystals. These compounds are monocyclic or polycyclic. All ring sizes have been studied from 5 to 12 as well as 14, 16 and 20, and the number of sulfur atoms in the -S - unit varies from 3 to 11. There are also systems with two independent -S - units ( = 2-8) in one ring, bridged by carbon atoms. The following are leading references bis-... 

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