Benzannulation bidirectional

A bidirectional benzannulation of the axial-chiral biscarbene complex 47 affords a bis-Cr(CO)3-coordinated biphenanthrene derivative 48, which combines elements of axial and planar chirality [49] (Scheme 31). Four diastereomers are formed in moderate diastereoselectivity, two of which have been isolated as the major isomers. 

A bidirectional benzannulation strategy allows the extension of an existing biaryl skeleton. The BINOL-derived bis-carbene complex 69, accessible through a sequence of regioselective double ortfio-lithiation/Fischer carbene complex synthesis, undergoes bidirectional benzannulation to give the dinuclear biphenanthrene complex 70. The optical induction exerted by the binaphthyl core is, however, only moderate a mixture of C2- and Cj-symmetrical bis(phenanthrohydroquinone) bis-chromium complexes is formed, in which the C2-... 

Bidirectional benzannulation of bischromium complex 81 with alkynes proceeds in a bisangular fashion to give - after oxidative work-up - enantiopure bisphenanthrene quinones 82 and 83 that undergo further cyclization upon subsequent ether cleavage by TMSI to afford [5]oxahelicene 84 (Scheme 11.26) [51]. 

Scheme 11.26 Bidirectional benzannulation ofBINOL-derived chromium biscarbenes to enantiopure bisphenanthrene quinones and [Sjoxahelicenes.

Scheme 11.27 Bisquinone functionalization of heteroheli-cenes via bidirectional benzannulation Bisangular versus angular-linear annulation.

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