Spiro rings

Carbocyclic spiro ring pairs generally are disconnected in two ways (1) one-bond... 

The synthesis consists of the same steps repeated and repeated, and can be extended to longer chains of spiro rings. 

Fig. 12.7. Alternate orientations of 3-methylbut-3-en-l-ol (3a) in the transition state for Ti-mediated epoxidation. Angle 9 is the inter-ring angle of the spiro rings. Reproduced from J. Org. Chem., 67, 1427 (2002), by permission of the American Chemical Society.

A further hetero-Diels-Alder reaction with inverse electron demand between o-QM 3 as the dienophile and either of the two diastereomers of spiro dimer 9 as the diene provided the spiro trimers 31 and 32 (Fig. 6.25). The absolute configuration was derived from NMR experiments. It was moreover shown that only two of the four possible stereoisomeric trimers were formed in the hetero-Diels-Alder reaction the attack of the o-QM 3 occurred only from the side syn to the spiro ring oxygen.28... 

Paritosh, D. R. et al Chem. Abs., 1994, 121, 35869j U.S. Pat. Appl. 42,229 Paritosh, D. R. etal., Phosphorus, Sulfur, Silicon Relat. Elem., 1994, 90(1-4), 175 This and several other compounds with fewer nitro groups and partial replacement of the spiro rings by halogen are patented as explosives. 

Tables 1-7 give representative examples, reported since 1995, of the major classes compounds containing a spiro phosphorus atom. The subdivision of classes of compounds is that used in CHEC-II(1996) the compounds are grouped according to the number and type of heteroatoms bonded to the spiro phosphorus atom. The labels k, l, m, and n represent the sizes of the spiro rings.

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... 

Satake M, Ofuji K, Naoki H, James KJ, Furey A, Mcmahon T, Silke J, Yasumoto T (1998) Azaspiracid, a new marine toxin having unique spiro ring assemblies, isolated from Irish mussels, Mytilus edulis. J Am Chem Soc 120 9967-9968 Scheuer PJ, Takahashi W, Tsutsumi J, Yoshida T (1967) Ciguatoxin isolation and chemical nature. Science 155 1267-1268... 

Reinstallation of the fractured spiro ring can be accomplished either directly at the enone level or, more interestingly, after the ketone carbonyl has been capped as in 36. When 36 and stereoisomers thereof are individually subjected to intramolecular oxymercuration, the stereochemical course of the cyclization is dictated by the approach of Hg2+ to that surface of the double bond where coordination to a proximal axially oriented ether oxygen can operate. [31] Where 37 and 40 are concerned,... 

The azaspiracids are another class of polyether toxins with unique spiro ring assemblies, a cyclic amine and a carboxylic acid. Five analogs have been described (Ofuji et al., 1999, 2001 Satake et al., 1998). Azaspiracids are produced by species of the dinoflagellate Protoperidinium, a phytoplankton genus historically thought to be benign (James et al., 2003a). 

The parent compound and a set of monosubstituted bis(acylamino)diarylspiro-X4-sulfanes (360 X = H, Me, MeO, Cl, NO2) undergo hydrolysis to the corresponding sulfoxides (361). The probable mechanism involves rate-determining cleavage of one of the S—N hypervalent bonds in the spiro ring with simultaneous proton transfer to the nitrogen atom. The hydroxide ion which is formed thereby then attacks the sulfur atom in a fast step to form a diaryl(acylamino)hydroxy-k4-sulfane (362), which is converted into the sulfoxide (361) (Scheme 47). ... 

The photochromic compounds of potential interest, based on the 2//-chromene ring system, are the 2//-benzopyrans (1.18) or the three isomeric naphthopyrans (1.19-1.21). However, 2H-naphtho[2,3-( ]pyrans (1.21) show little or no useful photochromic behaviour and can be discounted from any further discussion. Although R and can be part of a carbocyclic spiro ring, they are more commonly unconnected substituents such as gem dialkyl or aryl groups. 

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. 

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