Diallenes synthesis

Nevertheless, new examples have also been reported of allenyl sulfoxides [101] and especially allenyl trichloromethyl sulfoxides [39, Y+-X = S(0)CC13] [102]. There have been many trials to use these sigmatropic rearrangements for the synthesis of diallenes (compare 40 — 42), e.g. the reaction of the diols 43 with trichloromethane-sulfenyl chloride 44 to the diallenes 45 (Scheme 7.7) [103]. 

Since the synthesis of allenes from dihalocyclopropanes has been reviewed,130"132 only representative examples highlighting the process, along with the more recent results, are presented in this section. The formation of diallenes (equation 48) illustrates the usefulness of this process.133,134 Two other interesting examples are given in equations (49) and (50).133-137... 

Braverman, S., Duar, Y. Thermal rearrangements of allenes. Synthesis and mechanisms of cycloaromatization of it and heteroatom bridged diallenes. J. Am. Chem. Soc. 1990,112, 5830-5837. 

Not surprisingly, many of the methods which can be used in the synthesis of conjugated dienes can also be applied to dimerization of allenes. Thus, the bromoallenes (61) can be smoothly dimerized, for example, by treatment with 2 equiv. of copper(I) chloride in DMF at ambient temperature to give good yields of the diallenes (62). ... 

The first synthesis of this class of monocyclic diallenes has been reported by Sondheimer and co-workers (59, 60). They treated the dibromocarbene adduct 35 with (-)-sparteine-CH3Li complex at -10°C to obtain 36 (D2 symmetry), m.p. 113-116°C, [a] D +24.4°, together with the optically inactive meso 37 (C2h symmetry) m.p. 86-87.5°C. X-ray crystallographic data (61) have become available which show that the only isolable isomer of 1,2,6,7-cyclodecatetraene, m.p. 36°C (62), a lower homolog of 37 (X=H2), has a center of symmetry, indicating that this is a meso compound with C2h symmetry. 

The (15Z)-isomer of the diallenic compound mimulaxanthin (202) has also been synthesized (Chapter 3 Part IV) and the (9Z,9 Z)- and (9Z,9 Z,15Z)-isomers were obtained by direct synthesis via an analogous route from the corresponding allenic (Zj-Cis-aldehyde 39 [37] (Scheme 15). 

Scheme 1.32) [156]. Cu(II)-promoted intramolecular [2+2] cycloaddition of 1,4-diallenes 202 yielded bicyclooactadienes 204 however, under uncatalyzed thermal conditions, the authors noted that the formal [3,3]-sigmatropic rearrangement product, [4]dendralene 203, was formed m 50% yield. If optimized, this presents a nice method to form unsymmetrical [4]dendralenes, but relies on a lengthy synthesis of starting materials. 

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