Spiroannulated compound

The sequences of spiroannulation-secobromination or, better, spiroannulation-secosulfenylation offer great versatility for geminal alkylation as summarized in Eq. 123. The fact that spiroannulation of carbonyl compounds proceeds with stereocontrol converts these transformations into stereocontrolled carbonyl group elaborations. 

In spiroannulated polycyclic compounds, each fragment is described as an independent molecule. The names of these fragments are given in alphabetical order and are separated... 

Compound A//r(kcalmol ) MM2 A/7r(kcalmol ) exptl Strain energy (kcalmoL1) Strain energy of spiroannulation (kcalmoL1)... 

Diels-Alder cycloadditions of the readily available spiro[2.4]heptadiene (15) are a useful entry to spiro(cyclopropane-l,7 -norbornene) and related polycyclic compounds (equation 17)38. 1,1 -Diacetylcyclopropane was found to undergo unusual base catalyzed cyclizations resulting in spiroannulated cyclopropanes (equation 18)3,-4°. 

It was demonstrated in Section 3 that spiroannulation of cyclopropane to four- and higher-membered rings does not cause an increase in the strain energy of the molecule. It is not surprising, then, that the chemistry of these compounds does not differ from that of simple alkyl substituted cyclopropanes. Since exciting reviews on the chemistry of cyclopropanes are available42, the authors of this chapter will limit the description of properties of SPC of these types to some of their interesting applications. 

As demonstrated in Section IV, compounds possessing two spiroannulated cyclopropyl fragments could be successfully prepared by using double cyclopropanation or double cyclization of the corresponding bismethylene or bis(gem-dihalomethyl) precursors. 

Of special interest at present are phenolic compounds bearing suitable substituents which can undergo intramolecular cyclization induced by DIB. For example, whereas 4-hydroxybiphenyls normally gave in methanol the expected quinone ethers, when the aryl group had an o-alkenyl moiety, spiroannulated products resulted, with carbon-carbon bond formation [42] ... 

The treatment of bis(phenyliodonium)diyne triflates, 19 (n = 5,6,8), with sodium p-toluenesulfinate provides access to disulfones possessing spiroannulated or tethered cyclopentene rings (equation 57)86. However, because migration of the / -toluenesulfonyl group in the intermediate carbenes is competitive with insertion, the yields of the bis-cyclopentene compounds are relatively low, and disulfones of general structures 20 and 21 are also obtained. 

An oxidative spiroannulation reaction was carried out for simple phenols and as a result good yields of spiro-compounds containing tetrahydrofuran rings were obtained <02TL3597>. In the stereospecific and enantiospecific total synthesis of the sarpagine indole alkaloid dehydro-16-epinormacusine B, an oxidative cyclization of the alcohol shown below was the key and final step <02OL4681>. 

Allylic alcohols can serve as 7t-allyl cation precursors to act as electrophiles in Sn reactions with a tethered O-nucleophile giving rise to the formation of spiroannulated tetrahydrofurans <2000TL3411>. Michael acceptors are also suitable electrophiles for the cyclization to tetrahydrofuran rings <2003T1613>. The Tsuji-Trost allylation has found widespread application in the synthesis of carbo- and heterocyclic compounds. Allylic substitution has been employed in the stereoselective synthesis of 2-vinyl-5-substituted tetrahydrofurans <2001H(54)419>. A formal total synthesis of uvaricin makes twofold use of the Tsuji-Trost reaction in a double cyclization to bis-tetrahydrofurans (Equation 73) <20010L1953>. 

Reductive dehalogenation is an efficient method of synthesis of cyclopropanes spiroannulated to five- and higher-membered carbocycles (i.e. compounds in which spiroannulation does not result in accumulation of extra strain) . The required gem-(dihalomethyl)cycloalkanes are usually prepared by halogenation of the precursor diols (equation 1). The cyclization is most efficiently accomplished in the Zn-alcohol-water system . For example, spiro[2.5]octane 7 was prepared in 91% yield using this procedure. This method is useful even for a one-step preparation of bis-spirocyclopropyl compounds as exemplified in equation 2. However, the application of the reductive dehalogenation method to the synthesis of more strained SPC (i.e. spirohexane or spiropentane) often leads to rearranged products. For example, methylenecyclopentane was the only product obtained from bis(bromomethyl)cyclobutane (equation 3) ... 

Interesting compounds th bicyclic P-lactams (also those cyclic ethers, cyclic siloxj spiroannulated dihydrofuran organized by Cu(I). ... 

Interesting compounds that have been acquired from the metathesis process include bicyclic P-lactams (also those comprising a diene unit by the enyne metathesis ), a-stannyl cyclic ethers, cyclic siloxanes which can be opened to afford (Z)-alkenediols, spiroannulated dihydrofurans and dihydropyrans, and [2]catenanes from precursors organized by Cu(I). ... 

The reduction of tricyclic compounds containing a bicyclo[4.1.0]heptan-3-one structure has been proved to be a rather general access to the spiroannulated cyclohexanone systems. 

The synthesis of the 4 -spiroannulated ribonucleoside was aceomplished by elimination of the 2 -phenylthio group of compound 132 via a controlled oxidation with Davis oxaziridine reagent. 

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