Methylene cycloalkanes

The reductive cyclization of enynes has been used to prepare exo-methylene-cycloalkanes. Two systems have proven successful in this transformation, namely PMHS/Pd2(dba)3 CHCl3245 (Eq. 102) and Et3SiH/Pd(dppe)Cl2/HC02H (Eq. 103).246... 

TABLE 17. Structural parameters of ethene derivatives and small ring methylene-cycloalkanes (distances in A, angles in degrees)... 

Radialenes are a class of compounds that have only relatively recently been synthesized and described160-162. They may also be described as all-ew-methylene-cycloalkanes, and the first four members of this group of molecules, which we for the convenience of the reader, will refer to by the number of ring atoms, are presented in Figure 9. 

It is of course possible to name individual radialenes according to IUPAC rules [e.g. per(methylene)cycloalkanes 1-4]. However, the descriptiveness of the term radialene may some day pave its way into the official nomenclature. For substituted [ ]radialenes we have proposed1 a pragmatic numbering system, in which an inner ring is numbered first, followed by an outer ring . The numbering of substituents should follow IUPAC rules. Thus, the hydrocarbon 7 is 4,4-diethyl-5,5-dimethyl[3]radialene, the ester 8 should be called 7-methoxycarbonyl-5,5-dimethyl[4]radialene, the nitrile 9 which can exist in four diastereomeric forms is (6Z,7Z)-6-cyano-5,5,7-trimethyl[4]radialene and the difunctionalized [5]radialene 10 is (7 ,6Z)-7-bromo-6-formyl-6-methyl[5]radialene. 

Methylenecycloalkanes.1 A cycloalkene can be converted into a methylene-cycloalkane by the following steps hydroboration with 9-BBN and carbonylation-reduction2 to give a /i-(cycloalkylmethyl)-9-BBN derivative, which is then allowed to react with an aldehyde1 to form the final product. 

Table 4.10. 13C Chemical Shifts of Alkenes [90, 232-235], Dienes [233] and Methylene-cycloalkanes [236] (Sc in ppm).

Other methods to prepare alkanes Dichlorodimethyltitanium, 216 Alkenes (by type of alkene synthesized) [see also Alkenes (Methods to Form Alkenes) for general methods of alkene synthesis, Methylene cycloalkanes, Unsaturated carbonyl compounds]... 

Iodine-Mercury(II) oxide, 149 a-METHYLENE ALDEHYDES AND KETONES 1,4-Diazabicyclo[2.2.2]octane, 92 Dimethyl sulfoxide, 124 Formaldehyde, 136 Methoxyallene, 177 Methylene cycloalkanes By cyclization reactions Diacetatobis(triphenylphos-phine)palladium(II), 91 l-Hydroxy-3-trimethylsilylmethyl-3-butene, 147... 

The optically active aryl-methylene cycloalkanes and related compounds, shown in Figure 4, were designed by Schuster et al. as chiral, photobistable materials to be used in particular as chiroptical triggers for the control of liquid crystalline phases (see Section 5.5).[22]... 

These deuterium distributions were interpreted by assuming that in 11,12, and 13, rapid interconversions between a,y-diadsorbed and a,a,y-triadsorbed species, attached to the metal at the two gemdimethyl carbon atoms, were followed by metallocyclobutane dismutation. The resulting adsorbed methylene-cycloalkane may be deuterated via either n-alkyl or tertiary alkyl species. In the former case, rapid desorption would occur, with the formation of a d4 molecule, while in the latter case, a number of interconversions between cr-alkyl and 7r-olefinic cyclic adsorbed species would yield the perdeutero compound. In the case of demethylation at a tertiary center. 

Isolated overall yields were based on l,2-bis(methylene)cycloalkanes. GC yields are shown in parentheses. 

The absence of the formation of a five-membered ring at low temperature suggests that the initial attack of ethyl acetate occurred at the 2-position of the l,2-bis(methylene)cycloalkane-magnesium (1), followed by an intramolecular cyclization, generating the spiro intermediate (2). 

This new methodology is quite general and can be applied to the magnesium complexes of 1,2-dimethylenecyclopentane, 1,2-dimethylenecyclohep-tane, and 2-methyl-3-phenyl-l,3-butadiene. Likewise, other carboxylic esters, such as butyl and ethyl benzoates, can also be used to make various fused carbocyclic enols or p,y-unsaturated ketone products. Significantly, the overall synthetic process to form fused carbocyclic enols from the corresponding l,2-bis(methylene)cycloalkanes represents a formal [4+1] annulation. 

The sulphur and nitrogen heterocycles (80) and (81) have been prepared by hydroboration-carbonylation of bis-olefinic precursors, and the latter case is reported to be the first example of such a synthesis in the presence of a reducible functional group. Another hydroboration-carbonylation sequence has been used in the preparation of methylene cycloalkanes from cycloalkenes, and is shown in Scheme 11. ... 

Olefins may be converted in high yield to a-ahtoroketones by treatment with chromyl chloride in acetone. a-Carboxyketones, generally relatively inaccessible, can be prepared by treatment of ketones with lithium 4-methyl-2,6-di-tert-butylphenoxide and carbon dioxide. Cyclic ketones result from ring expansion of methylene cycloalkanes with cyanogen azide followed by hydrolysis, a procedure which complements the standard diazo-methane-ketone approach. Functionalized cis-bicyclic ketones can be synthesized by haloketal cyclizatlon followed by hydrolysis. ... 

Methylene cycloalkanes [e.g., methylene cyclopentane and methylene cyclohexane (MCH) (2S)j are structurally similar to isobutene. The polymerizations of these... 

---