Bredts rule

A potpourri of strained molecules and their associated strain energies (in kcal/ mol). 

A related issue is whether it is possible to incorporate an olefin at the bridgehead position of a bicyclic system. Extensive investigations have shown that there are substantial lim- 

Two views of a calculated structure for frufis-cycloheptene. The view on the left, sighting directly down the C=C bond, shows the substantial twisting in the carbon framework. Note, however, that the olefin is not only twisted a significant amount of pyramidalization occurs, as indicated by the structure on the right. The extent of pyramidalization is indicated by the three valence angles. At a planar center, these three will sum to 360°, which is clearly not the case here. 

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For a review on chiral anti-Bredt rule compounds see M. Nakazaki, Top. Cun. Chem. 125. 1 (1984). 

Among a variety of compounds whose molecular characteristics fall into this category, our current interests have further limited our discussion to the doublebond systems which may conveniently be classified as follows 1. chiral ( )-cyclo-alkenes, 2. chiral anti-Bredt rule compounds, 3. trans-doubly bridged ethylenes ( betweenanenes ), 4. bridged allenes, and 5. overcrowded olefins. 

Considering the impressive accumulation of review articles 42a f) on the Bredt rule and number of papers reporting exotic anti-Bredt rule compounds, it is rather sur-... 

The chiral C2-conformer 42 of a ( )-cycloalkene can transform into the enantiomeric Cf-conformer 44 through a planar Cs-conformer 43, and this rope jump racemization can be prevented by anchoring one end of the unsaturated center onto the ring by means of an extra-bridge. This bridging creates a bicyclic anti-Bredt rule compound 45, revealing that all anti-Bredt rule compounds (45) with one double bond are necessarily asymmetric (C, symmetry) and have one asymmetric carbon atom. 

Comparison of (—)-(R)-( )-cyclooctene (50) and the (—)-(S)-anti-Bredt rule compound 51 would suggest their close structural relationship, and this is reflected in their respective absolute rotation values 5,16b) [otJoabs —458° (neat) and —725° (CHC13) as well as in their respective (- )-Cotton curves [0] —1.4x 10s at 196 nm (cyclohexane) and —13.6 x 10s at 213 nm (isooctane). 

The ( )-cyclooctene moiety can also be seen in bicyclo [4.2.1]l(8)-nonene (53) and bicyclo[4.2.1]l(2)-nonene (54), the smallest isolable members among anti-Bredt rule compounds 48). 

Since a single anti-Bredt rule compound is neccessarily asymmetric, combination of two of them should afford double anti-Bredt rule compounds ( bridgehead dienes ) either of Cs (or Q) symmetry or of C2 symmetry depending upon the ways in which the enantiomers are combined to make up the molecules. 

While the achiral double anti-Bredt rule compound 56 50) of Cs symmetry was isolated in an impure state and was found to be very labile toward 02 and heat, the chiral 57 of C2 symmetry was assumed to exist very briefly in the pyrolysis of 3,6-dimethylidene-l,7-octadiene51). 

G. Kobrich, Bredt Compounds and the Bredt Rule, Angew. Chem. Int. Ed. Engl. 1973, 12, 464-473. 

The structures, including relative stereochemistry, of daphnezomines H (44), I (4S), J (46), and K (47), four new alkaloids possessing a daphnilactone-type (44 and 4S) or a yuzurimine-type skeleton (46 and 47) were elucidated on the basis of spectroscopic data [47]. Daphnezomine I is the first N-oxide alkaloid having a daphnilactone-type skeleton, while daphnezomine J is the first alkaloid possessing a yuzurimine-type skeleton with an anti-Bredt-rule imine [57,58]. 

Ormojanine (CLXIV) behaves analogously to panamine toward sodium borohydride. The NMR-spectrum of it evidences an olefinic proton and the Hofmann degradation product (CLXV) generates a diene which indicates 2 olefinic protons. The position of the double bond in CLXV violates the Bredt rule but the presumption is that the rule does not necessarily apply to rings of such size. 

Decarboxylation-dehydration. Marshall and Faublllc achieved the synthesis of bicyclo[3.3.1]-A -nonene (3), the most flagrant known violator of the Bredt rule, via the mesyloxy-acid (I). When this acid was treated with dimsylsodium in dimethyl... 

Bredt rule violation Antiaromatic ring Cumulene... 

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