Bicyclo heptenones

Fleming et a 1. have described full details of a route to the Corey lactone system that initially involves a [2+2] addition of dichloroketen and trimethyIsilylcyclopentadiene to give the bicyclo-heptenone (17). Regioselective electrophilic displacement of the silyl moiety gave the ether (18). Hydrodechlorination of (18) followed by Baeyer-Villiger oxidation gave the lactone (19) this lactone can be transformed into the Corey lactone (2c) in five steps. 

An interesting piece of work by Gelmi et al. showed that specific cycloaddition between 4-nitro-phenylazide and enamines 98a and 98b of 1,4,5,6-tetraphenyl-bicycloheptene-2-carboxaldehyde delivers spiro-bicyclo-heptenone-triazoles 99a and 99b. Enamines 98a and 98b were prepared in situ by addition of either morpholine or pyrrolidine to aldehydes 97a and 97b. Finally, rearrangement of spiro compounds 99a and 99b into triazole 100 occurred slowly in CHCI3 at room temperature (Scheme 31) [75]. 

It is interesting to note that the parent dienone 67 and its 2-methyl derivative 68, when irradiated in strongly acidic media, gave no product which would con espond to the protonated bicyclo[4,l,0]heptenone observed in the photolysis of protonated eucarvone. In FHSO3 at — 66°... 

Just one reaction has been described where lithiated methoxyallene 42 reacted with bicyclo[3.2.0]heptenone 175 to form the triquinane derivative 176 via a tandem oxy-Cope-transannular ring closure sequence (Eq. 8.31) [111]. However, cycloocta-none 177 was isolated as a major product, which is unusual since other alkenyl-lithium compounds and 175 provide only triquinanes. The authors assumed that the additional sp2-hybridized C-atom in the eight-membered ring intermediate (eno-late of 177) induces a conformation which is less susceptible to transannular ring closure. 

An unexpected, but potentially useful, reaction was discovered during attempts to effect Nef-like transformations of nitrobicyclo[2.2.1]heptenes into bicyclo[2.2.1]heptenones. Thus, treatment of 6-exo-aryl-5-endo-nitrobicyclo[2.2.1 ]hept-2-enes with SnCl2.2H20 in hot THF or dioxane led directly to 3-arylpyridines in moderate yield. 

One way in which a small company can keep abreast of new developments is to collaborate with universities. Moreover, such collaboration helps to motivate staff (and publication of results provides advertising). One fruit of such a collaboration was a synthesis of LTB4, in which chiral moieties of the molecule are derived from the enantiomers of a common intermediate (ll).11 Several routes have been devised for enzyme-catalyzed kinetic resolution of bicyclo[3.2.0]heptenones.12 An efficient one that was used for the synthesis of LTB4 (12) is shown in Scheme 29.4. 

The photolyses of conformationally fixed 3,y-unsaturated ketones can also be performed in constrained media. This was described for the ODPM rearrangement of bicyclo[2.2.1]heptenone and bicyclo[2.2.2]octenone in MY zeolites [47]. It is remarkable that direct irradiation of the guest-incorporated thallium-Y (TIY) zeolites at 254 nm resulted in higher yields of ODPM products than the triplet-sensitized solution photolyses (Sch. 19). This indicates that the triplet carbonyl species are generated more efficiently in the supercages of the zeolites presumably because of the presence of heavy... 

The possible intermediacy of an acyl alkyl biradical (e.g., [30]) in the photochemical reactions of cyclo-butanones has intrigued several researchers. Unlike Hostettler s results with bicyclo-[3.2.0]-heptenone [15]/ Erman observed that a-cleavage occurred on both sides of the carbonyl group of photoexcited bicyclo-[3.2.0]-heptenone [36] (21). This result might be anticipated if... 

While the bicyclo[2.2.1]heptenones and bicyclo[2.2.2]octenones are both excellent ODPM reactants, the higher homolog bicyclo[3.2.2]nonenones are rather reluctant regarding the 1,2-shift. In... 

Treatment of a, ) -unsaturated ketones with a-halo esters often results in oxirane (205) formation (Darzens reaction). However, the reaction of the dienone 203 with ethyl bromoacetate (204) produces the bicyclo[4.1.0]heptenone derivative 206 (equation 55) ... 

A superb example of the synthetic utility of the iodolactonization reaction in organic synthesis is the conversion of the bicyclo[2.2.1]heptenone below into the Corey lactone. The latter compound possesses four contiguous stereogenic centers and is an important precursor for the synthesis of prostaglandins. 

A deuterium-labeled bicyclo[4.1.0]heptenone system 14 has been used as a probe for the stereochemical course of the ring-opening reaction. Addition did not only occur across the cyclopropyl bond but also across the C —C double bond. 

Another useful method for the preparation of tropolone utilises the cycloaddition reaction of dichloroketene with cyclopentadicne to give a bicyclo[3.2.0]heptenone derivative which can be transformed into tropolone [251,252]... 

If the substituent is allylic and hence homoconjugative, intramolecular [2 + 2] cycloaddition is progressive to form bicyclo[3.2.0]heptenone as shown in Fig. 4 [19-23]. This is the second pattern of the ring transformation based on squaric acid. 

As a matter of fact, the above preparative reaction to obtain the framework of bicyclo[ 3.2.0 ]heptenone is already in hand. Indeed, the ring closure step after electrocyclic ring opening of 4-hydroxy-2-cyclobutenone is not limited to fully conjugated systems synthetic variants are realizable with other prox-imally placed ketenophUes. When an allyl group was located at C-4, the ketene underwent an intramolecular [2 + 2] cycloaddition reaction with this double bond to give the bicyclo[3.2.0]heptenone derivatives [111, 112[. 

Scheme 20 Different route to triquinane via oxy-Cope rearrangement of bicyclo[3.2.0] heptenone [107-110]...

Both bicyclo[3,l,l]heptenones and bicyclo[3,l,0]hexenones show bathochromic hypochromic u.v. spectral shifts relative to the corresponding bicyclo[3,2,l]octenone and monocyclic models. These shifts have been accounted for in terms of extension of the chromophore by the small ring, rather than by any distortion of the enone geometry induced by the presence of the small ring. 

The toluenesulphonylmethyl ketones (304) react with methanolic hydroxide to give a product mixture containing bicyclo[3,2,0]heptane derivatives (305) and (306). The bicyclo[3,2,0]hepten-7-ones (306) were shown to arise by rearrangement of the bicyclo[3,l,l]heptenones (307). The bicyclo[3,2,0]hepten-6-ones (305) are formed from (304) by a solvolytic mechanism. 

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