Spiro decane system

Studies directed toward the synthesis of bicyclomycin have resulted in the discovery of efficient routes to the construction of the 2-oxa-8,10-diazabicyclo[4.2.2]decane system (160). Thus, the monolactim ether (155) with a hydroxypropyl side chain at position 3, on oxidation with 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (DDQ), gave the product (156) in good yield, presumably via an iminium species (Scheme 51). No trace of the spiro compound (157) could be detected in this reaction. The formation of (156) is probably kinetically controlled. Prior protection of the alcohol as a silyl ether, followed by DDQ oxidation, gave the pyrazinone (158) subsequent deprotection and acid treatment gave the thermodynamically preferred spiro compound (159). The method has been extended to the synthesis of (160), having an exocyclic methylene this compound is a key intermediate in the total synthesis of bicyclomycin [88JCS(P1)2585]. 

Other investigators have used a new synthetic route103 in which the spiro[4,5]decane system is formed by condensation of a -dicarbonyl compound [e.g. (221)] with a cyclopropyl phosphonium salt (222).104 The bicyclic keto-ester (223) produced in this way was subsequently converted into ( )-anhydro-/3-rotunol (224), ( )-/3-vetivone (220), ( )-/3-vetispirene (225), ( )-linesol (226), and ( )-a-vetispirene (227) (Scheme 27). 03 An alternative approach to the vetispirane system involves Et[Pg.82]

The photocyclization of the enone (7) to yield (8) has been used as an approach to the synthesis of the spiro(4,5)decane system. The tetracyclic product (9a) is obtained from the photo-induced intramolecular cyclization of the pyridone (10a) Increase in the chain length involving (10b) resulted in the formation of... 

The spiro[4.5]decane system, found in a number of sesquiterpenes, continues to attract attention. One novel approach to this system utilizes the intramolecular addition of a carbanion to an arene tricarbonylchromium complex [e.g. (237) - (238)]. Decomplexation yields (239). 

Recently Yamada et afi described a facile method of preparing the properly functionalized spiro[4-5] decane system by acid catalyzed cyclization of cyclohexenone derivatives, and applied it to the synthesis of / -vetivone. The clever use of proximity effects is a noteworthy feature of this ingenious synthesis. 

Dioxaspiro[4.5]decane Figure 646 An example of a spiro ring system. 

Initial addition reaction of methyloxirane to 4-methyl-l-oxa-4-azaspiro[4.5]decane 164 is followed by ring expansion under thermal conditions. O-Nucleophilic attack is directed on quaternary carbon of the spiro system rather than on C-4 carbon of the oxazolidine ring, and 8,10-dimethyl-7,13-dioxa-10-azaspiro[5.7]tridecane 165 is a major product of the transformation (Scheme 42 <1995IZV1838>). 

Contrary to earlier work, Caldwell et al. conclude from a detailed study of the 4,4-dimethylcyclohex-2-enone-l,l-diphenylethene system, that the (2n + 2n) photocycloaddition arises from a triplet exciplex, and Crimmins et al. report that the enone (15) undergoes highly diastereoselective intramolecular photoaddition to give (16) which is a key intermediate in a new route to spiro[5.4]decanes. Similar intramolecular processes with other enones, followed by treatment with tributyltin hydride and AIBN, provide a convenient route to bicyclic compounds such as (17) in good yield (Crimmins et al.), and irradiation of the optically active silylallene (18) gives (19) with an ee in excess of 99% (Shepard and Carreira). 

Kuroda, C.. and Hirono. Y. Synthesis of spiro[4.5]decane ring system through allylsilane promoted spiroannulation, Tetrahedron Lett., 35, 6895, 1994. 

In a different approach to the spiro[4,5]decane ring system, Naegeli " has synthesized decanones of the type (228) by way of cationic cyclizations of appropriate a,/8-unsaturated ketones, e.g. (227). 

For a route to spiro[4-5] decanes based on intramolecular keto-carbene insertion in substituted cyclohexenes, see M. Mongrain, J. LaFontaine, A. Belanger and P. Deslongchamps, Canad. j. Chem., 48, 3273 (1970) and P. M. McCurry, Tetrahedron Lett., 1845 (1971). An interesting synthesis of spiro systems by o, a annelation of enamines has been developed by D. J. Dunham and R. G. Lawton, J. Amer. Chem. Soc., 93, 2074 (1971). 

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