Cyclic cyclohex

Cyclic a,) -unsaturated ketones present a rich array of photochemical reactions, some of which are of considerable synthetic value (see Section 6.4 of Part B). For cyclohex-enones, two prominent reactions are the di-rr-methane rearrangement (path A) and the lumiketone rearrangement (path B). 

Cyclic thioethers involving rigid linkages are also known. Examples include a range of derivatives of [14]aneS4 incorporating 1,2-benzene and/or 1,2-cyclohex-ane units 79 TTOB, TTMB 80 tetrathia and hexathia cyclophane derivatives.81 84... 

Another method using starting materials of type 20 includes ring closure via nucleophilic attack at cyclic ketones [60]. Thus, on treatment of compounds 36 with tetra-w-butyl ammonium fluoride (TBAF), the products 37 were isolated. If cyclohex-... 

Suitable cyclic carboxylic anhydrides for this process are for example cz5-l,2-cyclohexane-dicarboxylic anhydride (HHPA), cz5-l,2-cyclohex-4-ene-dicarbo-xylic anhydride (THPA), phthalic anhydride (PA), succinic anhydride (SA), 1-oct-2-ene-succinic anhydride (OSA), and glutaric anhydride (GA) - see Fig. 9. 

Ozonolysis of the O-methyl oximes of cyclic ketones in the presence of 1,4-cyclohex-anedione and ozonolysis of the O-methylated dioxime of 1,4-cyclohexanedione in the presence of cyclic ketones afforded the corresponding diozonides . 

In addition to the cyclodienes discussed above, the carboxidation of 1,3-cyclohex-adiene having conjugated double bonds was also tested. In this case, the reaction is strongly complicated by the Diels-Alder side reaction. The main part of the diene is consumed by the dimerization process, and only 25-30% is involved in the oxidation, yielding cyclic ketones. 

Homometathesis of cyclic alkenes affords larger rings. For example, cyclohex-adecadiene (57) was prepared by liquid-phase metathesis of cyclooctene (56) using WCl5/Et3Al [21], or in the gas phase by short-time contact of cyclooctene to a supported catalyst of Re207 activated with Me4Sn [22], Cyclohexadecenone (58), a muscone-type perfume, is produced commercially from 57 by selective oxidation. 

In the preparative application of [2 + 2]-photocycloadditions of cyclic enones to (substituted) alkenes, two factors concerning product formation are of decisive relevance, namely the regioselectivity and the (overall) rate of conversion. Regarding the regioselectivity in the addition to mono- and 1,1-disubstituted alkenes, Corey had shown that the preferred addition mode of cyclohex-2-enone to isobutene or 1,1-dimethoxyethylene was the one leading to—both cis- and trans-fused—bicyclo[4.2.0]octan-2-ones with the substituents on C(7) [8]. In contrast, in the reaction with acrylonitrile, the alternate orientation was observed to occur preferentially. Similar results were also reported by Cantrell for the photocycloaddition of 3-methyl-cyclohex-2-enone to differently substituted alkenes [14]. No significant differences in the overall rates of product formation for the different alkenes were observed in these studies. In order to explain these observed... 

Simple diastereoselectivities are observed in the reaction of cyclo-alkenones with cyclic alkenes, e.g., cyclopentene, wherein the transoid tricycle is formed preferentially. Whereas cyclopent-2-enone (7) affords 36 selectively, the more flexible cyclohex-2-enone (8) gives a 3 1 mixture of diastereoisomers 37 and 38 [7,61]. A stereogenic center in the cycloalkenone also has a strong impact on the product ratio as shown for the reactions of 4-alkylcyclohex-2-enones 39 and 40 with acyclic alkenes wherein the major diastereoisomer formed is the one in which the enone-alkyl group is trans to the new ring forming C-C bonds, i.e., 41t and 42t, respectively (Sch. 12) [62,63]. Cycloadducts 42 have been further converted to the pheromone periplanone-B. 

The reactivity of anions 433-436 with electrophiles has been studied by Shiner and coworkers. The cyclic derivatives 435 and 436 are relatively stable at —78 and —45 °C, respectively, the transformation of 2-lithio-l,3-dioxane 436 (generated from the corresponding precursor 439) into derivatives 440 occurring in high yields (Scheme 115)649. Michael addition to cyclohex-2-enone took place in the presence of CuI P(Bu-n)3 and BF3 OEl2. 

Cycloaddition of buta-1,3-diene to the C2 ligand affords 356, containing complexed cyclohex-l-en-4-yne, this time attached to an Ru3 face.538 With cyclopenta-1,3-diene, formal insertion of one of the C2 carbons into a C=C double bond occurs (possibly via a three-membered ring and ringopening) to give 357.539 Two molecules of the cyclic diene have been incorporated into the organic ligand, which shows C=C double bond disorder. 

Ozonolysis of 4,4-diphenyl-l-methyl-cyclohex-2-ene-l-ol in DCM at — 78 °C in the presence of AczO led to the oxygen-bridged 1,2-dioxocin 213 in 30% yield. Its formation is explained in terms of intramolecular trapping of the carbonyl oxide intermediate, followed by cyclic acetal formation. Since 294 is unstable and spontaneously decomposed to ketoaldehyde 215 (see Section 14.04.5.4), it was necessary to acetylate it in order to have the stable 1,2-dioxocin 213 (Scheme 60) <1995JA9927>. 

In the case of /J-pinene (Fig. 13), it is proposed that the protonic initiation creates a cyclic tertiary carbenium ion which rearranges into a more stable pendant species, and the successive addition-isomerization processes lead to a chain structure with alternating isobutyl and cyclohex-enyl subunits. The presence of one unsaturation per repeating unit has been confirmed by polymer analysis. 

AUylic oxidation. Cyclohexene is oxidized to cyclohex-2-enyl acetate in 75% yield by the reagent at 70° when catalyzed by potassium bromidefea. 8 hr.). The reaction is slow in the absence of a catalyst. Norbomene is unreactive, but bicyclo[3.2.noclene-2 is oxidized rapidly to about an equal mixture of endo- and cxo-bicycIo[3.2.1]oct-3-ene-2-yl acetates. Acyclic olefins or cyclic olefins prone to allylic rearrangement give a complex mixture of allylic acetates. 

The complex [OsHBr(CO)(PPh3)3] is effective for the selective hydrogenation of conjugated and non-conjugated dienes to monoenes, and this complex also catalyzes the hydrogenation of linear and cyclic alkenes. (-)-Carvone (9) is selectively reduced to 2-methyl-5-(l-methylethyl)cyclohex-2-en-l-one (10) or 2-methyl-5-(l-methylethyl)cyclohexanone (11), depending on the reaction conditions. ... 

Cyclic enamines have been reduced to alkenes with lithium aluminum hydride/aluminum chloride. The reducing efficiency of simple aluminum hydrides as well as chlorinated aluminum hydrides has been studied in detail, and AIH3 has been found to be the most effective for the conversion of cyclohex-enamines into cyclohexene (Scheme 48). ... 

Enolates of cyclic 1,3-diketones, such as 2-methyl-1,3-cyclopentanedione and 2-methyl-1,3-cyclohex-anedione, are especially prone to 0-alkylation because of their W geometry and steric hindrance at carbon. However, C-alkylations of these species can be conducted reasonably successfully in protic solvents, e.g. water.280 Trost and Curran have reported high yields for the C-alkylation of cyclic 1,3-diketones with allylic acetates in the presence of palladiumfO) catalysts and DBU (Scheme 80). 

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