Bicyclo hexenes

Suprafacial 1,3-shifts with inversion of configuration at the migrating carbon have also been observed in the thermal conversion of bicyclo[2.1.1]hexenes to bicyclo[3.1.0]-hexenes. ... 

Two different routes to PCs via bicyclo[3.1.0]hexane intermediates are shown. In route 1 stereo- and position-specific addition of dichloroketene to a bicyclo[3.1.0]hexene provided the framework for elaboration to prostanoids. Route 2 featured stereospecific internal cyclopropanation and stereospecific Sn2 displacement of carbon to establish the prostanoid nucleus. 

Trauner and colleagues [39] recently found a striking contrast in the thermal and catalyzed reactions of a triene. Thermal reaction of a trienolate readily underwent disrotatory electrocyclization to afford cyclohexadiene (delocalization band in Scheme 8) in accordance with the Woodward-Hoffmann rule. Surprisingly, treatment of the trienolate with Lewis acid did not result in the formation of the cyclohexadiene but rather gave bicyclo[3.1.0]hexene in a [4n +2nJ manner (pseudoexcitation band in Scheme 8). The catalyzed reaction is similar to the photochemical reaction in the delocalization band. 

Another example of a catalytic isomerization of 1,5-ene-ynes as 6/4-144 to afford bicyclo[3.1.0]hexenes as 6/4-145 was described by Toste and coworkers (Scheme 6/4.37) [318]. In this reaction, Pd or Pt salts gave only <5 % yield however, with Au salts the products could be obtained with excellent yield. 

Some of the bicyclo[3.1.0]hexene zirconocene derivatives, especially those containing a phenyl group, rearrange quantitatively to the corresponding 4-vinyl-l-metalla-2-cyclobutene derivatives when heated in toluene to 60-80 °C for several hours (equation 131). The 6,6-dimethyl-2,3-diphenyl-2-zirconabicyclo[3.1.0]hex-3-ene derivative prefers ring-opening to the isomeric j/. -allylic complex upon thermolysis. 

Irradiation 1-aza-diene 60 (Scheme 37) at ambient temperature with a Hanovia medium-pressure mercury lamp led to an interesting solid-state reaction [140]. The products obtained after 9 h of irradiation included a topochemical dimer 61 formed in 65% and a 1 1 mixture of epimeric bicyclo[3.1.0]hexenes 62 and 63... 

Cyclopropene can also be used as the aUcene component and affords bicyclo[3.1.0]hexen-2-ones upon reaction with alkyne dicobalt octacarbonyl complexes in the presence of NMO (Scheme 250). Vinyl ethers and vinyl esters serve as ethene equivalents in Pauson-Khand reactions. For example, reaction of vinyl benzoate with complex (169) furnished cyclopentenone (170) (Scheme 251). This reaction was used in a synthesis of (-l-)-taylorine and nortaylorine. Allenes participate in intermolecular Pauson-Khand reactions affording alkylidene-substituted cyclopentenones (Scheme 252). ... 

Propargylic acetates in equation (80) react differently in a process that also takes place via a 1,3-acyl migration. Thus, the reaction of such substrates gives bicyclo[3.1.0]hexenes, which can be transformed into cyclohexenones on treatment with K2CO3 in MeOH. As shown in equation (81),... 

Scheme 4 Formation of bicyclo[3.1.0]hexenes promoted by release of phenylsulfanyl...

Jullien and coworkers studied the cyclic voltammograms of variously substituted bicyclo[3.1.0]hexen-3-ones (Table 9) and found that the half-life times (ti/2 )are generally very short ( < lO"" s) except when the substrates were phenyl-substituted at C(4). In such cases the radical anions are very stable( 6 s) owing to the greater charge delocalization. A similar trend was found in some non-fused cyclopropyl ketones systems studied by House and coworkers. ... 

TABLE 9. Reduction potentials of substituted bicyclo [3.1.0]hexen-3-ones ... 

The later study of Cooke and Andrews on the parent bicyclo[3.1.0]hexene did not fully concur with the conclusions of Doering and co workers. The racemization of optically active bicyclo[3.1.0]hex-2-ene-2,4,4-d3 was found to occur 1.33 0.15 times faster than scrambling of the deuterium. Furthermore, the mechanistic quadrisection that Doering and Schmidt had achieved by resolution of optically active compounds, was in this case studied by introduction of a single stereospecific deuterium label on C(4) (see Figure 29). 

Bicyclo[2.1.1]hexene was reported by Bond and Scerbo to rearrange to bicyclo[3.1.0]hexene at about 180°C. Frey and coworkers found the activation parameters to be log A = 13.95, = 35.17 kcalmol" Roth and Friedrich studied the... 

An additional and noteworthy feature of the 3-allylcyclopropene photochemistry is side chain cleavage-recombination with retention of the three-membered ring. The photolysis of 246b delivers, in addition to the bicyclo[3.1.0]hexene 248b, the rearranged cyclopropenes 249 and 250. Homolytic cleavage of the cyclopropenyl-allyl bond and subsequent radical recombination at a phenyl-substituted centre accounts for these observations (equation 80). 

Under the same conditions, photolysis in benzene of 9,10-deoxytridachione (6), isolated from Tridachiella diomedea, " a marine mollusc, using a 450-W Hanovia lamp for three hours gave a simple photoproduct 7 (R = H) in 85% yield having the bicyclo[3.1.0]hexene ring system of crispatene (R = COEt) found in Tridachia crispata, another mollusc from the Caribbean. 

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