Ring systems spiro

This same concept applies to spiroannulations of six membered rings and is illustrated in a synthesis of acorenone B 155 as outlined in Scheme 547). The notion of alkylative carbonyl transposition permits the spiro enone 156 to become a logical intermediate. The standard analysis by a retro-aldol process translates the spiro ring system of acorenone B into a geminal alkylation problem as revealed by... 

The placement of the tether at the C(3) position of the nitronate provides access to the spiro mode of dipolar cycloadditions. This class has been evaluated for the preparation of five- and six-membered spiro ring systems (Table 2.54) (254). The dipolar cycloaddition proceeds in good yields with mild heating, however, the three-atom tether proceeds faster than the four-atom tether. 

A key step in the synthesis of 3-vetivone, a major constituent of vetiver, a perennial grass found in tropical and subtropical regions of the world, involved the reaction of compound A and dihalide B with two equivalents of LDA to form C. Draw a stepwise mechanism for this reaction. 3-Vetivone contains a spiro ring system—that is, two rings that share a single carbon atom. 

A fused ring system contains two rings that share a common carbon-carbon bond. A spiro ring system contains two rings that share one carbon atom. 

Spiro ring systems are named as spiro[x.y]aIkanes where the parent alkane corresponds to the total number of carbons in both rings, and x and y refer to the number of carbons that join the shared carbon (the spiro carbon), written in order of increasing size. When substituents are present, the rings are numbered beginning with a carbon adjacent to the spiro carbon in the smaller ring. 

Spiro ring system (Problem 23.55, Appendix B) A compound having two rings that share a single carbon atom. 

The second case in these examples demonstrates that high yields can be obtained for rather complex systems when using low catalyst loadings. An example of the rapid generation of a spiro-ring system for use as a pharmaceutical scaffold has been demonstrated by the Merck group. In this example, the starting materials are easily prepared in three steps (Eq. 6.8) [29]. 

The vinylbenzothiazoles can also function as very efficient Michael acceptors (78TL13). The a-lithio derivative of acetone dimethylhydrazone undergoes clean conjugate addition to the vinylbenzothiazole derived from cyclohexanone to provide, upon quenching the a-lithiobenzothiazole anion with methyl iodide and hydrolyzing the dimethylhydrazone group, the ketone (579) (93% overall, 86 14 cis trans). The pure cis keto benzothiazole was converted to the cis keto aldehyde (580), and then cyclized with p-toluenesulfonic acid to the A -3-octalone (581 Scheme 127). Many other examples of the use of this chemistry for the construction of fused and spiro ring systems have been developed. 

The first step starts off as a normal Fischer indole you just have to draw the molecules carefully to show the Spiro ring system, and you have to stop before an indole is formed as the quaternary centre prevents aromatization. 

Further evidence for the specificity of the interaction of UROS with the spirolactam 48 came when its two enantiomers were separately prepared by including a resolution step halfway through the synthesis [70]. One of the two enantiomers inhibited UROS at least 20 times more strongly than the other. The unsubstituted parent spiro ring system of 48 does in fact have a plane of symmetry and the difference between the enantiomers lies only in the arrangement of the acetate and propionate side-chains on the three pyrrolic rings of the macrocycle. This makes the discrimination shown by the enzyme between the two enantiomers all the more impressive. 

Type 2. Two rings with one common atom—spiro ring system... 

Substituents and functional groups are indicated in the usual ways. Spiro ring systems are always numbered smaller before larger, and numbered in such a way as to give the highest priority functional group the lower position number. 

Perhydrohistrionicotoxin (342) has been a simpler synthetic target. A recent formal synthesis of (+)-342 used a palladium-catalyzed carbonyl allylation to form the spiro ring system [720],... 

Since the most probable explanation for the failure of crinine and its derivatives to undergo the reactions characteristic of caranine is the presence of a spiro ring system in crinine, 5,10b-ethano-8,9-methy-lenedioxy-l,2,3,4,4a,5,6,10b-octahydrophenanthridine (CLXIII) was synthesized as a possible basic nucleus for the alkaloid. Cyanoethylation... 

The five coordinate spirophosphoranes have played an important role with respect to understanding the stereochemistry of four coordinate phosphorus reactions which proceed via phos-phorane intermediates. Variable temperature NMR studies have established the apicophilicities of a wide range of groups (i.e. relative preferences of a series of groups to occupy an apical position rather than an equatorial position of a trigonal bipyramidal (t.b.p.) conformation of a phosphorane). The spiro ring system has been used to stabilize transient reaction intermediates of acyclic compounds, for example hydrolysis intermediates such as hydroxyphosphoranes. 

The viscidanes exhibit an antipodal configuration at C7 compared to the bisabolane, serrulatane and decipiane diterpenes. This difference may reflect the involvement of a 3/ ,6 -acyclic precursor (211), or 3S,6E-, which cyclizes to the lS,7/ -intermediate (212) (Scheme 51). A 1,2-hydride shift with displacement of X would generate the tertiary carbocation (213) which could alkylate the Re-facc of CIO. The spiro-ring system produced (214) contains the 1,4-trans-disubstitution on the cyclopentane ring observed for the viscidane nucleus. A 1,5-hydride shift of the quasi-a ial allylic hydrogen in 214 and allylic rearrangement, with net yn-addition of water, completes the elaboration of the nucleus. Circumstantial support for the last step can be enlisted... 

The cedrene isoprenologues can also be generated from the carbocation (213).which, in this case, alkylates the Si-face of CIO in a lOZ-ene. The spiro-ring system produced displays the 1,4-cis- disubstituted cyclopentane ring. Further cyclization of this intermediate generates the tricyclic ring system of the 2-ep/-cedrene metabolites as shown in Scheme 52. 

Spiro ring systems. Ruppert and White have extended the study of synthesis of spiro carbocyclic systems by cleavage of cyclopropyl ketones (5, 41-42). In... 

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