Formals, bicyclic monocyclic

Bicyclic—monocyclic valence isomerization of a radical dianion in the bicyclo[3 1.0]hexanesemidione system has been demonstrated. Symmetrical 1,4-semldiones formally derived from cycloheptatriene and cyclobctatetraene perfer to exist in the bicyclic (4.1.0 and 4.2.0) structures. Bicyclic—monocyclic valence isomerization in the bicyclo[4.1.0]hept-3-ene-2,5-dione system occurs more readily for the dianion than for the radical anion. Several radical anions derived from the (CH)6 io annulenes are reported. In the case of the 1,2-oxygenated derivatives of (CH)io the dianions or radical anions are stable, but the diones undergo valence isomerization and under oxida-time conditions are converted to 4-hydroxynaphthalene-1,2-semiquinone. Enediol dianions in the bicyclo [2.2 l]hepta-2,5-dione and l-carbQalkoxybicyclo[3 2.1] octa-2,6-diene systems have been observed to undergo... 

The formal total synthesis of racemic guanacastepene (rac-187) from Snider and co-workers (Fig. 20) was submitted six months later than the completed synthesis of Danishefsky s group [116-118]. The shortest sequence developed by the Snider group utilized the sequential cuprate addition/enolate alkylation of 2-methylcyclopent-2-enone 90 previously exploited by Piers, Williams and Danishefsky (Schemes 15 and 31). As outlined in Figs. 19 and 20, the strategies of Danishefsky and Snider are closely related. Both rely on stepwise annulations to build up the tricyclic ring system. They differ only in respect to the particular reactions that converted the monocyclic starting material (90) via bicyclic hydroazulenes (207 vs 227) into the desired tricyclic 5-7-6-system (224). 

Today the family of 1,3-heterophospholes contains monocyclic 1,3-azaphospholes (5), 1,3-oxaphospholes (6), 1,3-thiaphospholes (7) and 1,3-selenaphospholes (8), as well as the benzo derivatives (1), (2), (9) of (5)-(7) and a naphtho derivative (10). While the benzo derivatives (1) result formally from the 4,5-anellation to (5), 1,5- and 1,2-aneUation leads to two isomeric bicyclic systems such as (11) and (12) with a bridgehead nitrogen atom. Strictly speaking they therefore belong in Volume 8. However, they are also described here as they are closely related to the monocyclic... 

MonolerpeneB. M. may be considered formally as dimerization products of isoprene (2-methyl-1,3-butadiene, CsHg) and have a C,o skeleton. For biogenesis, see teipenes. The class of M. includes not only acyclic but also mono- and bicyclic hydrocarbons and their oxidation products (alcohols, aldehydes, ketones, and acids). Tri- and tetracyclic M. are very rare. The simplest acyclic M. are geraniol and nerol (see geraniol), from which mono- and bicyclic M. are formed by intramolecular cyclization. The most important caition skeletons of the monocyclic M. are illustrated in formulae 1-6. 

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