Saturated Carbocyclic Ring Synthesis

General Methods. - A review of the preparation and chemistry of silyl substituted cyclopropanes, an area which has been unusually quiet during the period under review, will be of general interest. Despite this, amongst the novel routes to cyclopropanes reported is one involving the treatment of an a-haloketone (1) with 

A cation radical chain cyclopropanation reaction has also been described using ethyl a-diazoacetate (2), to give reasonable yields of useful three-membered rings. A full account of the Lewis acid catalysed [2++4] polar cycloaddition reaction of the methylthio chloride (3) with a 1,3-diene is of interest/ as is a study of the 

General Methods.—The intramolecular coupling of dicarbonyl compounds to cycloalkenes by low-valent titanium is an exceptionally mild and useful route to 4—16-membered ring carbocycles. Baumstark et ai have now shown that, in 

The enormous potential provided by the Simmons-Smith reaction is further demonstrated in an efficient one-pot synthesis of spiro-compounds of the type (10) by reaction of cyclic enol-silyl ethers with diethylzinc-methylene iodide this remarkable synthesis ca. 70% overall) proceeds via the three sequential reactions (7) (8), (8) (9), and (9)— (10). The versatile dichlorocarbene species is most conveniently generated under phase-transfer conditions using either KOBu -crown or NaOH-PhCHzNEts Cl. 

Allylsilanes have enjoyed widespread use as reagents in allyl-transposition reactions with electrophiles [i.e. ( )- (12)]. Now Sakurai et aV have found that the corresponding homoallylsilanes (13) can be used in the synthesis of cydopropyl ketones (14) from acid chlorides in the presence of Lewis acids. 

Cyclopropane adducts prepared from the addition of dibromocarbenes to alkene substrates are proving to be extraordinarily valuable intermediates in the synthesis of alternatively substituted cyclopropanes. A number of workers have now demonstrated the stereoselective substitution of the bromine atoms for alkyl groups using alkyl copper re agents. 

Full details have been given for the preparation of chloro(phenyl)carbene (3), from the corresponding diazirine, and for its subsequent trapping by /3-methylstyrene, leading to the cyclopropene (4) after dehydrochlorination. An excellent new catalyst for the synthesis of cyclopropanecarboxylates (5), from olefins and diazoesters, is the rhodium cluster compound, Rh6(CO)i6. In general, good yields of (5) are only obtained if a large excess of olefin is used, but other work 

Chiral cyclopropanes, such as (9), have been obtained by degradation of (+)-a-pinene using a sequence of reactions that features a stereocontrolled ring contraction of a cyclobutanol derivative/ The iron carbonyl complex (10) has been resolved, and used to prepare the optically active cyclopropanes (11).  

The thermal hexa-1,4-diene l-methyl-2-vinylcyclopropane ( homo-ene ) equilibrium usually lies well to the left, presumably because of ring strain, but by the simple expedient of incorporating a hydroxy substituent in the hexadiene (16), cyclopropyl aldehydes (17) can be obtained in good yields. In related work, Dauben et al. have shown that medium-sized cyclic trienes can be thermally isomerized to tricyclic compounds e.g. (18).  

Enamines (19 n =3-12) undergo nucleophilic attack by succinimide to give the fused cyclopropanes (20) subsequently, the two heterocyclic substituents can be displaced by various nucleophiles.  

This Report covers developments in the synthesis of saturated and partially unsaturated carbocyclic compounds during 1976 carboaromatic systems are not included. 

The well-known synthesis of cyclopropanes from allylic halides by hydroboration, followed by base-catalysed cyclization of the intermediate y-chloroborane (1), has 

The Favorski-type reaction of cyclic chloroenamines has provided an elegant entry into bicyclic cyclopropanes, but hitherto the method has not been applied to 

Cyclopropanations of alkenes with alkyl diazoacetates are catalysed by rhodium(ii) carboxylates, and Sasaki et al have shown that crown ethers have several advantages over quaternary ammoniurq ions for the catalytic synthesis of allene-cyclopropanes from addition of allene-carbenes to olehnic substrates. 

The appearance of a Symposium-in-Print on aspects of carbene chemistry is obviously relevant to those interested in cyclopropane chemistry. Sonication reactions are becoming increasingly popular 

2-Lithio-2-phenylsulphonylpropane (5) acts as an alkylidene transfer reagent in reactions with a,B-unsaturated esters to allow the facile preparation of gem-dimethyIcyelopropanecarboxylie 

The addition of 2-nitropropane tp o-cyanoacrylates, under the influence of base, proceeds to give the acid component of the 

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