Alkyl cyclopropanes

The changes in the length of a C—C single bond may be interpreted as an effect of hybridization. An analysis of XD data indicates that the bond from the cyclopropyl ring to a substituent can be described approximately as an sp2 22 hybrid9, and the mean C—C bond length between the C3 ring and a C(sp3) atom is 1.519(2) A. 

FIGURE 4. Hexacyclopropylethane (22) molecule projected down the central C—C bond. Drawn after Reference 57 

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Das aus dem (a-Halogen-alkyl)-cyclopropan-System mit Organo-zinnhydriden gebildete Radikal kann sich zum entsprechenden Allyl-Radikal umlagern, oder es stellt sich ein Gleichgewicht ein z. B.6 ... 

Alkyl-cyclopropane aus 3-Athoxy-alken-(l)-en allgemeine Arbeitsvorschrift4 Eine aquimolare Mischung von 3-Athoxy-alken-(l) und Bis-[2-methyl-propyl]-aluminiumhydrid wird unter Stickstoff 6—8 Stdn. bei 85-90° am RiickfluB und danach 1-2 Stdn. bei 160-180° am absteigenden Kiihler erhitzt. Als Riickstand erhalt man Athoxy-bis-[2-methyl-propyl]-aluminium. 

I-Butene 4.4-Dichloro-4-fluoro-l-phenyl- ElOa. Ill [(1-OH-alkyl) — cyclopropane + HF]... 

TABLE 2. Structural parameters of alkyl cyclopropanes and bicyclopropyl derivatives ... 

Hexanal 3-Isopropenyl-5-methyl-E17e, 2535 (3-CHO-2,2-R2-l-alkyl-cyclopropan/A)... 

Some of the most striking evidence for the intermediacy of protonated cyclopropanes comes from studies of the reaction of cyclopropane and alkylated cyclopropanes with acetyl chloride and aluminum chloride. 

As illustrated in Fig. 20.1, the C-C bond that is broken in the hydrogenolysis of alkyl cyclopropanes is that one between the two least substituted carbon atoms of the ring. With unsymmetrical 1,2-dialkyl-cyclopropanes (1, R iR ) the bond adjacent to the smaller alkyl group is preferentially cleaved. When coupled with the facile cyclopropanation of alkenes, the hydrogenolysis of alkyl cyclopropanes over platinum oxide has served as a useful means of introducing a methyl group onto a tertiary carbon atom as illustrated by the preparation of tert-butyladamantane (3) (Eqn. 20.1) and the 9-methyldecalins, 5 and 6 (Eqn. 20.2). > ... 

This difference in reactivity is particularly significant since l-(l-methylseleno)- -vinylcyclopropanes are formed even 31) from 1-(1-methylseleno)-l-(l -hydroxy-2 -(phenylseleno)alkyl)cyclopropanes (Scheme 45 b, f) for the first time the phenyl-selenenyl rather than the methylselenyl moiety is removed in the process. 

If the reaction takes place via an anion or in a S 2 fashion, high yields of the product alkyl-cyclopropanes have been obtained. Thus, reaction of methyl 4,6-( -benzyIidene-2,3-dideoxy-2,3-C-[(7 )-(chloromethyl)ethylidene]-a-D-mannopyranoside (1) with lithium aluminum hydride in refluxing tetrahydrofuran gave methyl 4,6-0-benzylidene-2,3-dideoxy-2,3-C-isopropylidene-a-D-mannopyranoside (2) in 89% yield. Similarly, treatment of chloromethylcyclopropane 3 with lithium triethylborohydride, followed by oxidation with pyridinium chlorochromate,. gave ishwarone (4) in 75% yield. ... 

The dialkylamino substituent in [a-(dialkylamino)alkyl]cyclopropane 1 was converted to the corresponding 7V-oxide 2 using 3-chloroperoxybenzoic acid and heat. Intermediate 2 then underwent a Meisenheimer rearrangement to give 2,3-benzoxazepine 3. ... 

In analogy to the mono-alkylated cyclopropanes annulated cyclopropanes gave methylated cyclic products 10, 11,and 12 upon catalytic hydrogenolysis. 

The formation of metalated cyclopropanes is primarily the reason for the inefficiency of de-hydrohalogenation of cyclopropyl monohalides with strong base. This reaction yields for the most part alkylated cyclopropanes, e. g. formation of 24 with allene 25 as the minor product. 

Haloalkyl)cyclopropanes, and [(phenylselanyl)alkyl]cyclopropanes 1 are cleanly reduced by organotin hydrides to the corresponding hydrocarbons 2 in efficient chain processes. 

The bisammine complexes are prepared by condensing dry ammonia at low temperatures onto I Oxygen ligands such as 1,4-dioxane, THF or DMF can be used as well. Simple alkylated cyclopropanes can be converted to the corresponding tetrameric platinacyclobutanes on reaction with chloroplatinic acid in ethyl acetate , rather than in acetic anhydride ... 

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