Spiroannellation

Organobis(cupratesY, spiroannelation.16 1,4-Dilithiobutane, prepared from 1,4-dichlorobutane and lithium in ether at 0°, on reaction with copper thiophenoxide (2 equiv.) forms a biscuprate, formulated as 1 for convenience. This dimetallic reagent adds to 3-halo-5,5-dimethyl-2-cyclohexenones (2) to form the spiro-[4.5]decanone 3 in yields as high as 96%. Cuprates prepared from other Cu(I) sources are less efficient, as is the cuprate prepared from di-Grignard reagents... 

SPIROANNELATION OF ENOL SILANES 2-OXO-5-METHOXYSPIRO[5.4]DECANE (Spiro[4.5]decan-1-one, 4-methoxy-)... 

The new spiroannelation method gives, by use of both the tin and silicon chemistry, ready access to [4.4], [4.5], [5.5], [4.6], and [5.6] spirocyclic systems as well as five-, six-, and seven-membered rings possessing a quaternary center. An in situ oxidation, or protection of an initially formed crude secondary alcohol increases the ease of isolation of the product and leads to improved overall yields. Furthermore, for symmetrical substrates, this chemodifferentiates two oxygen functionalities at... 

Alkylation at carbon positions activated by electron-withdrawing groups is illustrated by the spiroannelation of cyclopentanone and cyclohexanone by sonication of the parent compound with potassium t-butoxide and 1,4-dibromobutane (Eq. 3.22). The so-nochemical improvement is especially large with cyclopentanone which is normally particularly prone to self-condensation [119]. 

With 4-phenyl-1,2,4-triazoline-3,5-dione (180), bicyclopropylidene (1) reacted by yet another mode and gave the spiroannelated diaziridine 182 (Scheme 40)... 

The recently determined kinetic data for the bromination of bicyclopropylidene (1) and spirocyclopropanated bicyclopropylidenes 55, 56 in methanol at 25 °C disclose that the addition of Br2 onto the double bonds in 1,55,56 proceeds essentially with the same rate as the bromination of corresponding oligomethyl-ated ethylenes. The bromination rate increases with an increasing number of spiroannelated three-membered rings, and the rate of bromination correlates with the TT-ionization energies of the molecules (Table 5) [134]. 

Spiroannelation. A new method for intramolecular spirocyclizalion involves decarboxylation of w-halogeno-j8-keto esters with lithium chloride in HMPT at 125— 140°. The method appears to be fairly general.1 Examples ... 

Spiroannelation.2 Acylation of 1 by the cnol lactone 2 results in formation of only one (3) of the two possible spiro[4.5]decenes. The hulky isopropyl group is... 

Benzofuranones exhibit a carbonyl band near 1710 cm-1 (63CB1680, 75JHC1051). The effect of spiroannelation at the 2-position has been much studied (82JCS(P1)403, 63JCS1814). 2(3//)-Benzofuranones exhibit a carbonyl band near 1830 cm-1 (CCU) (82UP31000). Trippett reports that alkyldibenzofurans exhibit a characteristic band at 1217— 1189 cm-1 (57JCS419). 

Intramolecular Grignard Reactions. Some chemists use the reactivity of a substituent in the Grignard reagent to generate the desired product. For example, a one-step spiroannelation reaction has been developed by taking advantage of a dihalide or a cyano-halide reactant (92—94). 

The formation of flavenes by the reduction of 2-hydroxychalcones undoubtedly proceeds via the alcohol and constitutes a simple but useful synthesis (67JCS(C)1933). This route has been developed (68AJC2247) and extended to spiroannelated compounds (99). 

The dimerization of o-quinone methides in which one molecule acts as the heterodiene and another as dienophile leads to spiroannelated chromans (equation 12). The driving force for this considerable tendency to dimerize is associated with the ease with which the... 

Reaction of chlorotrimethylsilane with hydroxymethylspiroepoxycyclohexadienone (279) affords the spiroannelated chroman (280) (Scheme 73) (80TL4973). The proposed mechanism invokes a quinone methide intermediate which dimerizes to the chroman. 

The synthesis of some 2,2-spiroannelated chroman-4-ones from o-hydroxyacetophenone and a cycloalkanone in the presence of a secondary amine has been described (78S886). The reaction has also been used to prepare a range of chromanones bearing non-identical or... 

The dilithio derivative of N-methyl-o-toluamide reacts with aromatic aldehydes and ketones to give hydroxyamides. Thermal cyclization affords 3-phenylisochroman-l-ones (64JOC3514). Spiroannelated isochromanones result when the organolithium compound reacts with fluorenone or alicyclic ketones. 

Spiroannelation Boron trifluoride etherate, 43 Triphenyltin hydride, 335 Stork-enamine reaction (see Alkylation reactions)... 

Spiroannelation via Organobis(cuprates) 9,9-Dimethyl spiro[4.5]decan-7-one. 

Reactions of a 2-benzazepin-l-one derivative involving a spiroannelation procedure from 76 to afford the spiro-cyclic 3-benzazepine derivative 83 via 77-82 have been reported (Scheme 9) <2005H(65)1359>, while other chiral substituted 2-benzazepines have been prepared from D-glucose via furo[3,2-f][2]benzazepine derivatives <2005S2307>. 

The electrochemical behavior of ///-dihydroionol 44 is interesting. The ester 44 (R = Ac) is unusually inert to the oxidation, however, the alcohol 44 (R = H) smoothly undergoes electrolytic spiroannelation and pyran-ring formation leading to 47 (70%) and 61 (18%) in an MeCN/H20-Et4NC104/MgS04-(Pt) system (Scheme 3-22) 69 70>. 

Organobis(cuprates), 14, 225. A detailed report14 of the spiroannelation of enones with these cuprates includes 11 examples. In all cases yields of 56-96% are obtainable. 

The reaction of steroidal ketones with Lawesson s reagent led to the spiroannelation of the 1,3,2-dithiaphos-phetane nucleus on the tetracyclic ring system <2003PS2003>. 

---