Preparation and structural study of naphtho- and anthrocyclobutene derivatives which have extremely long C–C bonds

Organic Solid-State Reactions

“…Exceptions are solid butatrienes that stereospecifically give the radialene upon heating [148], or the further examples in Ref. [149], or 1-phospha-allenes [150]. In addition, the solid-state milling of C 60 with KCN catalysis to give 18% of C 120 appears to be a [2 + 2]-dimerization (not shown in Scheme 18) [151].…”

“…The highly substituted tetraallene shown in Scheme 23 undergoes the solid-state double [2 + 2]-cyclization thermally (180 ∘ C) to give the dicyclobuta[b,g]anthracene with very long C-C bond (1.726 Å) in the cyclobutene moieties [149]. The linear racemic s-trans-diallene must undergo a conformational change within the crystal prior to the cyclization to yield the in,in-and out,out-dimethylenecyclobutenes with quantitative yield in a 1 : 1-ratio.…”

Cyclization reactions of bis(allenes) for the synthesis of polycarbo(hetero)cycles

“…The 45 synthesis of anthracyclobutene derivatives 19 via crystal-tocrystal thermal [2+2] cycloaddition of compounds 20, involving bis(allene) intermediates 21 has been reported (Scheme 8). 16 Probably, rotation of the bulky diarylallene groups is necessary for the cyclization reaction. 50 Analogously, propargyl phosphites and propargyl phosphinates are also feasible substrates to obtain allenes via [2,3] It was proposed that bis(tricycles) 42 and 49 were formed from bis(β-lactam-allenynes) precursors, via formation of tetraradical intermediates.…”

Organic Solid-State Reactions with 100% Yield

“…If an excess of HX gas was applied to 185 the pure compound 137a or 137b was obtained (Scheme 24). 130 G. Kaupp…”

“…These cyclizations can be performed on a hot stage at 180°C for 30 min and the macroscopic shape of the crystals does not change at least for the octaphenyl case [130]. Importantly, the tetraphenyl-substituted benzocyclobutene bonds of 411 exhibit the extraordinary length of 1.726 Å [130], which is the world record for sp 3 -sp 3 single bonds [131] (Scheme 65).…”