Spirocydes

Lithiation/electrophile trapping of enantiopure epoxide 209 stereoselectively gave epoxide 211 further elaboration via a metalated epoxide gave spirocydic epoxide 212, which after treatment with acid gave epoxylactone 213 as a single dia-stereomer (Scheme 5.49) [74]. 

An interesting observation was made when o-aminophenol (2-411) was employed in the reaction with carbethoxypiperidone 2-410 and acrolein (Scheme 2.98). In this case, the spirocydic scaffold 2-412 was exclusively formed in 67% yield. This result can be explained by invoking a stereoelectronic control due to the presence of the aromatic ring which prevents the formation of the corresponding fused tetracyclic isomer. Moreover, both reactive sites can simultaneously be functionalized using 2-amino-1,3-propanediol (2-413) as partner in the multicomponent reaction. This leads to the formation of three new cycles... 

The domino process probably involves the chiral enamine intermediate 2-817 formed by reaction of ketone 2-813 with 2-815. With regard to the subsequent cy-doaddition step of 2-817 with the Knoevenagel condensation product 2-816, it is interesting to note that only a normal Diels-Alder process operates with the 1,3-bu-tadiene moiety in 2-817 and not a hetero-Diels-Alder reaction with the 1-oxa-l,3-butadiene moiety in 2-816. The formed spirocydic ketones 2-818/2-819 can be used in natural products synthesis and in medidnal chemistry [410]. They have also been used in the preparation of exotic amino adds these were used to modify the physical properties and biological activities of peptides, peptidomimetics, and proteins... 

Spirocydic hydrocarbon (Section 3.14) A hydrocarbon in which a single carbon is common to two rings. 

Finally, in the case of alkoxy-substituted allenyl benzyl ketones 51, the spirocydes 52 are obtained (Scheme 11) [36],... 

Kiyota H (2006) Synthesis of Marine Natural Products with Bicydic and/or Spirocydic Acetals. 5 65-95... 

Astarita, A., Cermola, F., Iesce, M.R., and Previtera, L. (2008) Dye-sensitized photooxygenation of sugar fiirans novel bis-epoxide and spirocydic C-nudeo-sides. Tetrahedron, 64 (28), 6744—6748. 

Demuth, M., Palomer, A., Sluma, H.-D., Dey, A.K., Kruger, C., and Tsay, Y.-H. (1986) Asymmetric photocydoadditions with optically pure, spirocydic enones. 

Hasegawa et al. [85] have explored the electron transfer-promoted regioselective ring opening of cyclopropyl silyl ethers 183 for the generation of cyclopropoxy radical 185 which, upon intramolecular radical cyclization, leads to the formation of spirocydic compound 184 in moderate yields (Scheme 8.51). 

Sofikiti, N., Tofi, M., Montagnon, T., Vassilikogiannakis, G. and Stratakis, M. (2005) Synthesis of the spirocydic core of the prunolides using a singlet oxygen-mediated cascade sequence. Organic Letters, 7 (12), 2357-2359. 

Another mild method for cleaving spirocydic OrS,5-orthoesters uses a mixture of iodine and sodium bicarbonate in a heterogeneous mixture of ether and water to give the lactone [Scheme 2A 18]+242... 

Stockman and coworkers [329] developed a straightforward synthesis of a tricyclic compound 2-636 which has some resemblance to the spirocydic portion of the natural product halichlorine (2-637) [330], On treatment of the symmetrical ketone 2-633, accessible in five steps from alcohol 2-632, with hydroxylamine hydrochloride the spiro piperidine 2-636 could be obtained in 62% yield (Scheme... 

MgS04, the tetracycles 2-648 were obtained with excellent diastereoselectivity in reasonable yield. The reaction presumably starts with a condensation of the aldehydes 2-645 with the benzyl-protected amine moiety of 2-644 to give an iminium ion which can subsequently cyclize to afford the spirocydic intermediates 2-646. A [3,3] sigmatropic Cope rearrangement then forms the nine-membered cydic enamines 2-647 which, after protonation, act as the starting point for another indole iminium cyclization to provide the tetracycles 2-648 via 2-647. 

Leeper FJ (1994) Evidence for a spirocydic intermediate in the formation of uro gen III by cosynthetase. In The biosynthesis of the tetrapyrrole pigments. Ciba Foundation Symposium, vol 180. Wiley, Chichester, pill... 

A second form of optical isomerism analogous to that shown by organic spirocydic compounds has been demonstrated. Any molecule will be optically active if it is not superimposable on its mirror image. The two enantiomers of bis(ben-zoylacetonato)beryllium are illustrated in Fig. 12.3. In order for the complex to be chiral, the chelating ligand must be unsymmetric (no/ necessarily asymmetric or chiral, itself) [Be(acac)2] is not chiral. 

Scheme 6.9 Polycyclization via Mizoroki-Heck reaction buiiding spirocyde 22.

Cheng has demonstrated that spirocydic cyclopentadienes such as 61 may be produced upon treatment of an iodoalkene with an Iqme (Scheme 41).I 1 A mechanism involving oxidative addition of nickel(O) to the iodoalkene followed by two sequential allquie insertions has been proposed. 

Scheme 6.18 A hydrostannylation-cyclization-anion capture process leading to a spirocydic skeleton [76].

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