Nine-membered ring

Nine membered Rings.—The cis- and tra/w-fused acyloins (222) were isolated from an attempted acyloin condensation of diester (223).  

A short review of regio- and stereo-specificity in cyclization of medium-ring 1,5-dienes has appeared. The cis,rrans-cyclononanol (224) cyclized via the chair-like conformation shown to give (225) on treatment with iV-bromosuccinimide-  

The chlorohydrin derived from the oxidoketone obtained by potassium permanganate oxidation of caryophyllene oxide has been assigned structure (226) on the basis of an 2f-Ray structure analysis.  

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A fundamental set is also called a smallest set. Usually such a smallest set is selected that it also contains the smallest rings the smallest set of smallest rings (SSSR). This makes chemical sense in indane (Figure 2-38a), for example, where only the six- and the five-membered rings are of chemical significance whereas the enveloping nine-membered ring is not. 

When K.yba, Cram and coworkers attempted the synthesis of dibinaphthyl-22-crown-6 from binaphthol and diethylene glycol ditosylate. the reagent ratio was as described either by V or X (Eqs. 3.1 or 3.3). The intent was to make the 22-membered ring. Some of the 11-membered ring was isolated as well (Eq. 3.5). None was apparently observed for the benzo case because the nine-membered ring is less favorable. In short, it is not the intent of the synthesis but the reaction dynamics which determine the product. 

The course of alkylation is also influenced by the steric arrangement of the enamine. 1-Pyrrolidino-l-cycloheptene gave approximately equal quantities of the C- and N-alkylated products in dioxane, while 1-pyrroli-dino-l-cyclooctene, and 1-pyrrolidino-l-cyclononene afforded N-alkylated products exclusively under similar eonditions (29). The reason for N alkylation in the eight- and nine-membered ring compounds is to be found in the conformation of these rings, which prevents full interaction of the unshared electrons on nitrogen with the n eleetrons of the double bond. 

II. Cycles of Medium Size (Seven- to Nine-Membered Rings)... 

Other advances include the construction of seven- and nine-membered rings via the analogous [4-1-3] and [6-1-3] cycloadditions with dienes and trienes respectively. Heterocycles, such as tetrahydrofurans and pyrrolidines, are accessible using carbonyl compounds and imines as substrates. The following discussion is organized around these recent discoveries. It serves to illustrate the versatility and the high degree of selectivity which are some of the distinctive features of the Pd-TMM chemistry. 

Nine-membered ring systems are potentially accessible via a TMM cycloaddition with conjugated trienes in a [6-1-3] fashion. However, tropone is the only reported system that undergoes such a reaction. Interestingly, these cydoadditions are remarkably selective in that only nine-memhered ring products are formed. 

Scheme 34 Formation of the central nine-membered ring and completion of the carbon skeleton in Hirama s improved total synthesis of the marine neurotoxin ciguatoxin CTX3C (183)[90b]...

Eor reviews of 76 (X = N) and other nine-membered rings containing four double bonds and a hetero atom (heteronins), see Anastassiou, A.G. Acc. Chem. Res., 1972,5, 281, Top. Nonbenzenoid Aromat. Chem., 1973,1,, Pure Appl. Chem., J975, 44, 691. For a review of heteroannulenes in general, Anastassiou, A. G. Kasmai, H.S. Adv. Heterocycl. Chem., 1978, 23, 55. 

Bovio, B., Bonati, F. and Banditelli, G. (1984) X-ray crystal structure of tris[p-3,5-bis (trifluoromethyl) pyrazolato- N, N ] trigold(I), a compound containing an inorganic nine-membered ring. Inorganica Chimica Acta, 87, 25-33. 

Several aspects of this reaction are intriguing. Despite the relatively high temperature (105° C), the nine-membered ring seems to have a strong influence on the stereoselectivity. The tendency for planarity at the ester bond may also contribute to the stability of the TS. 

The reaction in Entry 8 was used in the synthesis of members of the phomoidrides. The cyclohexene ring that is constructed creates a bicyclo[4.3.1]skeleton containing seven- and nine-membered rings. 

Entry 8 was used to create the central nine-membered ring system found in the diterpene jatrophatrione. Entry 9 is an example of a boronate fragmentation (see p. 899). Entry 10 illustrates enolate fragmentation. The reaction presumably proceeds... 

Molecular models indicate that cavitand (259) has a tall, vase-shaped architecture in which the four benzene rings and four nine-membered rings combine to form a concave cavity to which is attached the four diazanaphthalenes (Moran, Karbach Cram, 1982). The latter groups resemble flaps which may occupy either equatorial or axial positions. In the former arrangement, the inner surface area of the cavity is quite reduced and hence a considerable decrease in the inclusion ability of this form is expected. 

Following their studies on the trapping of intermediates in the [5 + 2]-cycloaddition with CO, which led to the [5 + 2 + l]-process, the Wender group found that when related reactions were conducted with aryl alkynes under an atmosphere of CO, a novel four-component [5 + 2 + 1 + l]-product was observed.172 A VCP, an alkyne, and 2 equiv. of CO react to give the biaryl compounds shown (Scheme 78) via the formation of a nine-membered ring intermediate. 

The mechanism of this novel process is proposed to involve formation of a nine-membered ring, which after tautomerization undergoes an electrocylic ring closure to form the bicyclo[4.3.0]nonadienone intermediate. Elimination of ROH gives the aromatic product observed (Scheme 79). 

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