Spiro-ring Compounds

The formation of the tetrazine is interpreted in terms of an initial [3 -I- 2] cycloaddition leading to unstable spiro compounds. Ring opening of the dihydro-1,2,3-triazole ring generates the zwitterions... 

Nitro-substituted indolino spiroben2opyrans or indolino spironaphthopyrans are photochromic when dissolved in organic solvents or polymer matrices (27). Absorption of uv radiation results in the colorless spiro compound [1498-88-0], C22H2gN202, being transformed into the colored, ring-opened species. This colored species is often called a photomerocyanine because of its stmctural similarity to the merocyanine dyes (see Cyanine dyes). Removal of the ultraviolet light source results in thermal reversion to the spiro compound. 

The acetoxy dienone (218) gives phenol (220). Here, an alternative primary photoreaction competes effectively with the dienone 1,5-bonding expulsion of the lOjS-acetoxy substituent and hydrogen uptake from the solvent (dioxane). In the case of the hydroxy analog (219) the two paths are balanced and products from both processes, phenol (220) and diketone (222), are isolated. In the formation of the spiro compound (222) rupture of the 1,10-bond in the dipolar intermediate (221) predominates over the normal electron transmission in aprotic solvents from the enolate moiety via the three-membered ring to the electron-deficient carbon. While in protic solvents and in 10-methyl compounds this process is inhibited by the protonation of the enolate system in the dipolar intermediate [cf. (202), (203)], proton elimination from the tertiary hydroxy group in (221) could reverse the efficiencies of the two oxygens as electron sources. 

In a formal synthesis of fasicularin, the critical spirocyclic ketone intermediate 183 was obtained by use of the rearrangement reaction of the silyloxy epoxide 182, derived from the unsaturated alcohol 180. Alkene 180 was epoxidized with DMDO to produce epoxy alcohol 181 as a single diastereoisomer, which was transformed into the trimethyl silyl ether derivative 182. Treatment of 182 with HCU resulted in smooth ring-expansion to produce spiro compound 183, which was subsequently elaborated to the desired natural product (Scheme 8.46) [88]. 

Okada, M. Ring-Opening Polymerization of Bicyclic and Spiro Compounds. Vol. 102, pp. 1-46. 

Formation of the six-membered ring on cyclization of the ( )- and (Z)-4-nonenylhydroxylac-tams [E)-4 and (Z)-4 in formic acid, occurs completely stereoselectivcly to afford the 6.6-spiro compounds (7R )-5 and (7S )-5, respectively51,52. The reaction supposedly proceeds via a chair-like transition state, as depicted. Depending on the reaction conditions, however, 0.5 % 2 or about 25%51 of the five-membered ring isomers are also formed. 

A second mole gives spiropentanes. In fact, any size ring with an exocyclic double bond can be converted by a carbene to a spiro compound. ... 

Spiro compound (18), also containing two fIve-membered rings, can be made by oxidation of the acyloin (19) (Chapter T24). 

Based on a known synthesis of spiro compounds with six-membered rings [63] we succeeded in the stepwise assembly of terminal substituted mono-[64] and dispiranes [65]. Hereby the cyclisation of the dibromide 35 with TOSMIC (Iter. 1) is the keystep of the reaction sequence as the initial ketone functional group (36) is recovered. Four subsequent reactions led to the spirodibromide 40 (Iter. 2). Final spirocyclisation afforded the dispirane 41, representing a precursor for new calamitic liquid crystals (Fig. 16) [66]. 

An interesting strategy for the synthesis of pyrrolizidines and indolizidines has been developed by Brandi and co-workers. Cycloaddition between nitrones or nitrile oxides with methylenecyclopropanes generates strained tricyclic spiro compounds, which are prone toward further transformations, such as rearrangement, ring opening, and new ring closure (Scheme 10.17).116... 

Diisobutylaluminium hydride catalyses the ring-closure of various dienes. It is proposed that the process involves addition of the aluminium hydride to a terminal double bond, followed by ring-closure and, finally, elimination of the catalyst (equation 106). Thus 1,5-hexadiene gives methylenecyclopentane (213) (equation 107), 1,6-heptadiene gives methylenecyclohexane (214) (equation 108), 4-vinylcyclohexene gives bicyclo[3.2.1]oct-2-ene (215) (equation 109) and the spiro compound 217 is obtained from 5-methylene-l,8-nonadiene (216) (equation 110)112. 

Addition of carbenes to Jt-electron excessive aromatic compounds, or those which possess a high degree of bond fixation, is well established. Dihalocarbenes react with naphthalenes with ring expansion to produce benztropylium systems (Scheme 7.8). Loss of hydrogen halide from the initially formed product leads to an alkene which reacts with a second equivalent of the carbene to yield the spirocyclopropyl derivatives in high yield (>95%) [14, 50]. Insertion into the alkyl side chain (see Section 7.2) also occurs, but to a lesser extent [14]. Not unexpectedly, dichlorocarbene adds to phenanthrenes across the 9,10-bond [9, 10, 14], but it is remarkable that the three possible isomeric spiro compounds could be isolated (in an overall yield of 0.05% ) from the corresponding reaction with toluene [14]. 

Apparently, the driving force for the ring opening is the relief of the strain in the spiro system and the formation of the stable carbonate double bond. The double ring opening is probably a concerted process from the initial radical addition product to the open-chain radical. Even though the spiro compound XI is an allyl monomer, it does copolymerize with a wide variety of comonomers. 

Photolytic. When propachlor in an aqueous ethanolic solution was irradiated with UV light (>, = 290 nm) for 5 h, 80% decomposed to the following cyclic photoproducts W-isopropyloxindole, W-isopropyl-3 hydroxyoxindole, and a spiro compound. Irradiation of propachlor in an aqueous solution containing riboflavin as a sensitizer resulted in completed degradation of the parent compound. 3-Hydroxypropachlor was the only compound identified in trace amounts which formed via ring hydroxylation (Rejtb et al, 1984). Hydrolyzes under alkaline conditions forming W-isopropylaniline (Sittig, 1985) which is also a product of microbial metabolism (Novick et al., 1986). 

However, it is also possible to visualize spiro compounds with groupings that are not aU different, where enantiomeric forms exist because mirror image compounds are not superimposable. The diamine shown is chiral, in that the mirror image forms are not superimposable, even though only two types of ring. 

We have met diosgenin as an example of a natural spiro compound (see Box 3.17), and further examination of the structure shows the double bond as in cholesterol, a second five-membered ring c/s-fused onto the five-membered ring D, as well as the spiro fusion of a six-membered ring. Before this structure dismays you, take it slowly and logically. It should not be too difficult to end up with the stereodrawing shown here. 

The conformations of spiro-compounds containing the oxane ring have been reported (Scheme 5) (81CJC1132). They exist only in conformation 9a at room temperature at lower temperature, no indication of a second conformer was found. The methyl-substituted derivatives 10a and similar tricyclic analogs occur in the same conformation 11a. 

In the benzyl-substituted spiro compound 30 (Scheme 18), the phenyl ring (due to a weak intramolecular interaction) was folded over the 1,3-dioxan-3,6-dione moiety (78M1263) the ABMNX spin system in the H NMR spectrum therefore was analyzed in detail (in CDCI3). 

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