Bredt, anti

Chromium aminocarbenes [39] are readily available from the reaction of K2Cr(CO)5 with iminium chlorides [40] or amides and trimethylsilyl chloride [41]. Those from formamides (H on carbene carbon) readily underwent photoreaction with a variety of imines to produce /J-lactams, while those having R-groups (e.g.,Me) on the carbene carbon produced little or no /J-lactam products [13]. The dibenzylaminocarbene complex underwent reaction with high diastereoselectivity (Table 4). As previously observed, cyclic, optically active imines produced /J-lactams with high enantioselectivity, while acyclic, optically active imines induced little asymmetry. An intramolecular version produced an unusual anti-Bredt lactam rather than the expected /J-lactam (Eq. 8) [44]. 

Still another example is the easy formation of anti-Bredt bicycloalkenones (see p. 188). As indicated above, a,a -dihalophosphoranes can be used to prepare 1,1-dihaloalkenes. Another way to prepare such compounds is to treat the carbonyl compound with a mixture of CX4 (X Cl, Br, or I) and triphenylpho-sphine, either with or without the addition of zinc dust (which allows less Ph3P to be used). " ... 

Reaction of l-aroyl-2-aryl-3a,6a-diazapentalenes 105 with 1 equiv of DMAD in the presence of Pd/C is reported to provide 3% yield of 107, presumably via the corresponding primary adduct 106 <1966PNA1385>. The reaction with more than 2 equiv of acetylene dicarboxylates affords surprisingly unusual anti-Bredt s adducts having the... 

Compounds with at least one stereogenic center and one stereogenic axis (this also includes anti-Bredt-olefins that exist in two stable atropisomeric forms). 

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). 

Of particular interest is the syn-l,6-imino-8,13-methano[14]annulene (59) which represents the first authenticated example of a stable 1H-azepine with a free NH group (80AG(E)1015). The annulene with aluminum oxide undergoes a remarkable isomerization to the anti isomer (61). Investigation shows that the isomerization is not a thermal reaction but involves alumina-catalyzed proto tropic shifts via the 3/7-azepine tautomer (60). This system is unique in that it is the first example of a 3H -> 1H azepine tautomerism, and is a consequence of the high degree of strain in the anti-Bredt 3iT-azepine (60). 

The ionization potential, 8.69 eY, is lower than in the case of -cyclooctene (8.98 eV) or cyclohexene (9.12 eV), as expected. The highly strained anti-Bredt olefin, 11-bromo-e/ -9-chloro-7-ethoxybicyclo[5.3.1]undec-l(ll)ene has been synthesized and its struc-... 

Anomeric effect, 82, 310-311, 305 Antarafacial, 163 examples, 164 sigma bonds, 167 Anti-Bredt olefin, 102 Approximations of MO theory Born-Oppenheimer, 22 Hartree-Fock, 222 Huckel, 35, 86 independent electron, 35 LCAO, 229 nonrelativistic, 22 SHMO, 87... 

Give a mechanism for this transformation which does not involve anti-Bredt intermediates. 

This result suggests that the anti-Bredt s rule olefin if may be an isolable compound. A number of bicyclic bridgehead olefins (e.g. 52) have recently been prepared, and their stabilities related to the corresponding frans-mono-cyclic olefins 11S>116). The stability of 51 should correlate, then, with the... 

Wudl et al. [283] obtained the ring-opened TV-MEM-ketolactam 153 by self-sensitized photo-oxygenation of. V-methoxyethoxymethyl (MEM)-substituted [5,6]azafulleroid 151 (Scheme 61). The reaction is highly regioselective, most likely because the anti-Bredt carbon-carbon double bonds in 151 are more strained. 

In this section, zinc reductions, which have been found in the course of chemical studies on isodaphniphylline (8), and isolable and non-isolable anti-Bredt s rule imines are described. 

Generally, bicyclic compounds (71) containing a bridgehead double bond and with S 5 7 may be regarded as an anti-Bredt s rule compound, which is quite unstable because of high ring strain energy (33). 

In 1967, two American groups first succeeded in the synthesis of bicyclo[3.3.1]non-l-ene, an anti-Bredt s rule olefin (72) (34). Since then several isolable anti-Bredt s rule olefins with S = 7 have been prepared (35). The heterocyclic anti-Bredt s rule compound was first produced... 

Reed and Lwowski (38) have done the photolysis of 1-azidonor-bornane (84) in MeOH and obtained two amines (85 and 86) in 54 and 24% yields, respectively. In the course of intramolecular nitrene rearrangements, an anti-Bredt s rule imine, 2-azabicyclo[3.2.1]oct-l-ene (87), can be regarded as a plausible intermediate from which the amine 85 is produced. On the other hand, a biradical 88 has been... 

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