Unsaturated bicyclo heptanes

Thus, the predictions seem to be in conflict with the observed syn biases. However, along the trajectory of attack of the nucleophile to the carbonyl group of the bicyclo[2.2.2]octane structures (indicated in 23 and 24), out-of-phase interactions between the reagent and the substrate are involved, and this is different from the situation in the bicyclo[2.2.1]heptane structures (15a) [83-87]. Thus, attack on the side opposite to the unsaturated moiety will be favored. This is a kind of SOI (Fig. 3a) which unsymmetrizes the n face. 

Other examples of the synthesis of cyclobutanes with abstraction of an allylic hydrogen are the photochemical formation of tricyclo[4.1.0.03,7]heptan-5-ones (e.g., 5) from norborn-5-en-2-ones33 and of bicyclo[4.2.0]octenes (e.g., 7) from doubly unsaturated ketones.34... 

Bicyclo[4.2.0]octan-7-ones 7, substituted at C8, resulted from addition of 7-lithio-7-methoxy-bicyclo[4.1.0]heptane to saturated and unsaturated aldehydes and subsequent rearrangement.146148... 

Bicyclo[3.2.0]heptane-l,5-diols are oxidized by Jead(IV) acetate35,36 or sodium periodate35 to give cycloheptane-1,4-diones. With lead(IV) acetate in acetic acid at 100 C substrates with a hydroxy group in -position to one of the newly formed carbonyl groups eliminate water to afford a,/ -unsaturated cycloheptanediones,36 and / ,y-double bonds migrate to the apposition.35... 

The intramolecular cyclopropanations of a-diazocarbonyl compounds have been extensively studied and recently reviewed . The reaction is satisfactorily accomplished when the diazo carbon atom is proximal to the double bond in the substrate. Thus, the construction of bicyclo[3.1.0]hexane and bicyclo[4.1.0]heptane skeletons has been achieved by this method, whereas the synthesis of bicyclo[5.1.0]octane or the larger bicyclic systems has usually been difficult (equation 73). Bicyclo[2.1.0]pentan-2-ones expected in the reaction of j8,y-unsaturated diazoketones are generally labile and readily undergo the ring cleavage to give jS,y-unsaturated ketenes. ... 

Bicyclo[3.1.0]hexan-2-one and bicyclo[4.1.0]heptan-2-one were obtained from the corresponding unsaturated diazo ketones with 75 and 95% ee, respectively, when the chiral bis(semicorrinato)copper(II) catalyst developed by Pfaltz (see Section 1.2.1.2.4.2.6.3.2.) was used, ° whereas Aratani catalysts, in general, provided low to moderate enantioselectivities for these transformations. " Modest ee-values (35-40%) were also observed when the Pfaltz catalyst was applied to unsaturated /1-keto-a-diazo esters such as methyl 2-diazo-3-oxohept-6-enoate and -oct-7-enoate. ° ... 

A tandem ring expansion followed by cyclization of l-(trimethylsiloxy)bicyclo[4.1.0]heptanes substituted with unsaturated side chains at C5 has been developed for the construction of bicyclo[5.3.0]decane ring systems, e.g. conversion of 19 to 20. ... 

From a practical point of view ketals derived from 1,2-diphenyl- 1,2-ethanediol (hydrobenzoin) are most useful because the diastereomeric ratios are very high and the auxiliary is available in both enantiomeric forms. In addition, most of the derived cyclopropanes are crystalline and their diastereomeric purities can easily be improved by recrystallization from diethyl ether62. Thus, (l/<,65 )-bicyclo[4.1.0]heptan-2-one is available with >99% ee by hydrolysis of recrystallized (l.R,4, S, 5, S, 6,S)[4, 5 ]diphcnylspiro[bicyclo[4.1.0]heptane-2,2 -[l, 3 ]dioxolane]62. The Sim-mons-Smilh reagents add to related ot,/3-unsaturated ketals derived from cyclopentenone, cycloheptenone and a bicyclic enone, also with similarly high diastereoselectivities62. 

Fig. 10 Towards new mechanophores for bond creation the bicyclo[3.2.0]-heptanes. The alpha, beta-unsaturated ester formed from mechanically induced [2+2] cycloreversion can undergo subsequently react with nucleophiles (a), such as thiols to form functionalised copolymers left) and cross-linked gels (right). Analysis of the stereoisomerism of the products (b) supported a stepwise mechanism for the ring-opening via a 1,4-diradical intermediate...

Koizumi and coworkers have developed a new enantiomerically pure a,p-unsaturated sulfoxide dienophile bearing the isoborneol group as a chiral auxiliary, dimethyl (f )-2-(10-isoborneolsulfinyl)maleate (214), which has been successfully employed as a chiral synthetic equivalent of dimethyl acetylenedicarboxylate [174], The dienophile (214) underwent cycloaddition with cyclopentadiene, in the presence of zinc chloride, with high stereo- and diastereoselectivity (92% single endo diastereoisomer, 6% single exo diastereoisomer) to yield the major cycloadduct (215), which was subsequently transformed into the half-ester (216), an intermediate in the syntheses of (-)-aristeromycin (199) and (-)-neplanocin A (200). Cycloadduct (215) has also recently been used for the synthesis of bicyclo[2.2.1]heptane lactone (217) [175,177], which itself is an intermediate in the synthesis of the iridoid (-)-boschnialactone [176] (218) (Scheme 5.69), and also in the formal synthesis of (-)-aristeromycin (199) and (-)-neplanocin (200) [177]. 

Bicyclo[3,2,0]heptane Derivatives.— These are principally prepared by the [2 -I- 2] cycloaddition of a cyclopentene with another unsaturated unit. Typical combinations which have been routinely applied in syntheses are photochemical addition of a cyclopentene to an olefin or acetylene and thermal addition of a cyclopentadiene with an olefin, a keten, or an acetylene. In the last case, cycloaddition with an alkyne is complicated both by competition between [2 -h 2] and [2 + 4] modes of addition and by the possibility of a second addition of cyclopentadiene to the initially formed bicyclo[3,2,0]heptadiene. The results for diphenylacetylene and cyclopentadiene are shown in Scheme 31. 

The bicyclo[2,2,l]heptane system also continues to find employment for the assessment of new synthetic procedures, or for testing the efficacy of new reagents. Isolated yields of 50—65 % of ap-unsaturated aldehydes have been obtained by reaction of alkyl tosylhydrazones with butyl-lithium, addition of DMF, and hydrolysis however, reaction of camphor tosylhydrazone (381 X = NNHTs) according to this procedure only gave 10 % of the aldehyde (382 X = CHO), presumably because of unfavourable steric effects. " Trimethylsilyl trifluoromethanesulphonate is a mild reagent for converting carbonyl compounds into trimethylsilyl enol ethers, for example the production of (382 X = OSiMcj) from camphor (381 X = Experimental details... 

Bicyclo[3,l,l]heptanes.—Preparations of bicyclo[3,l,l] heptanes by solvolytic rearrangements of bicyclo[2,2,l]heptanes are noted later. Formation of bicyclo-[3,l,l]heptan-6-ones by solvolytic displacement, for example (157) from (158), is a well established route and is further exemplified by conversion of (159) into (160) and of (161) into (162). The possibility that products are formed via unsaturated ketens by [2 + 2] cycloaddition has been considered.Keten (163), independently generated, did undergo cycloaddition but to give (164), and so it is unlikely that bicyclo[3,l,l]heptanones such as (157) are formed via the keten. 

The structure of products obtained by the reaction of allylsilanes with a,P-unsaturated carbonyl compounds also heavily depends on the type of the carbonyl group and the size of silicon substituents of allylsilane reagents. Thus, the reaction of allyl(trimethyl)silane with 1-acetylcyclohexene gives mainly conjugate allylation products with a small amount of bicyclo[4.3.0]heptanes derived from [3 + 2]... 

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