Cyclopropylallene

Finally, there has also been research into the ozonolysis of allenes. Thus sterically hindered allenes react by transfer of one oxygen atom, forming a mixture of reaction products214. Recently, the ozonolysis of a cyclopropylallene has been shown to yield a diastereomeric mixture of cyclopropyl esters215. 

Generally, cycloproylallenes are prepared by the same methods as employed for the synthesis of other allenic hydrocarbons. Thus, cyclopropylallene (17) itself has been obtained from vinylcyclopropane (139) via its dibromocarbene adduct 140 using the DMS method (Scheme 5.19) [54],... 

With substituted vinylcydopropanes, the corresponding cyclopropylallenes are formed in comparable yields [55],... 

In principle, the direct cydopropanation of vinylallenes and related substrates also allows the preparation of cydopropylallenes. However, because of low or no discrimination between the differrent double bonds, complex product mixtures are to be expected. A case in point is provided by 1,2,4,5-hexatetraene (12), which yields the cyclopropylallene 149 on diazomethane/CuX treatment - but only in a (difficult to separate) mixture with all other cydopropanation products of 12 (Scheme 5.21) [61]. 

Scheme 11 Cyclopropylallenes as precursors for 2-aryl-1,3,5-hexatrienes and their subsequent [4 + 2] cycloadditions [53,54]...

Two 1,1-divinylcyclopropanes that have attracted a great deal of interest are 43 and 44. The microwave structure of the first has been obtained and, based on the photoelectron spectrum and STO-3G calculationsa strong electron delocalization from the ring has been implicatedConjugation was also present in 44, but through conjugation of the cyclopropyls was not prominent. Cyclopropylallenes such as 45 behaved similarly to vinylcyclopropanes, with no evidence for interaction of the cyclopropyl with the second double bond ... 

Conjugated cydopropylcyclopropylidenes do not undergo ring expansion but rearrange to cyclopropylallenes, e.g. formation of 133 and 135. ° ... 

Addition of thiophenol to cyclopropylallene 12, a less common method for the preparation of cist tram mixtures of divinylcyclopropanes, is used in the synthesis of karahanaenone850, an odoriferous constituent of Japanese hop and cypress oil. Karahanaenone is also prepared via a silyloxy-Cope rearrangement of 15 in 54% overall yield (starting with isobutyraldehyde and a mixture of cis- and /rpyridinium chlorochromate oxidation to give 14)851-852,... 

Cyclopropylallene (55) and a number of alkyl substituted products have been investigated. In Fig. 16 we derive the h est occupied MO s of 58 from those of an allenic moiety and a cyclopropylmoiety. As anticipated there is essentiaily the same interaction between the cyclopropane ring and the adjacent double bond... 

The difunctional additions of electrophiles and nucleophiles to 1-cyclopropylallenes have been investigated. In the presence of NCS and NaCl, 2,6-dichloro-l,3-hexadiene was formed in good yield (eq 44). ... 

Roth examined the kinetics of the isomerization of cyclopropylallene to 3-methylenecyclopentene and found log A = 14.08 — 50200/2.3 7.Furthermore, c/5 -2-deuterio-l-allenylcyclopropane undergoes geometric isomerization 4.5 times faster than rearrangement (Scheme 7.53). 

Reduction of organomercurials formed from cyclic allenes (10—14-membered rings) with sodium borohydride yields an increasing ratio of trans. cis monosubstituted olefins as the ring size is increased. The stereochemistry and mechanism of the reduction of cyclic allenes using di-imide and sodium in liquid ammonia have been investigated. A stereospecific reduction with sodium in liquid ammonia of the intermediate cyclopropylallene... 

The cyclopropyl ring is another popular motive for the construction of halogenated dienes. Under the influence of haloniums, 1-cyclopropylallenes 253 undergo a halohydroxylation and provide 2-haloolefine 254 in medium to good yields (Scheme 99) [195]. The stereoselectivity, which tends to be mainly or exclusively ZZ, is significantly affected by the nature of the substituents. 

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