Spiro octane

Diels-Alder reactions of 2-(trimethylsilyloxy)allylidenecyclopropane (112) with electrophilic dienophiles gives 3-silyloxy spiro[2.5]oct-2-enes or the corresponding hydrolysis compounds spiro[2.5]octan-3-ones (Tables 11 and 12) [32]. 

Cyclic diazoalkanes have been used to generate spirocyclopropanes via ring contraction of pyrazolines formed in the initial cycloaddition step. Two novel examples are the transformation of 3-diazo-2-nitromethylenepiperidine (16) into 5-aza-spiro[2.5]octane 17 (45) and the conversion of 1-diazo-2-methylenecyclo-propane (18) into methylene-spiro[2.2]pentane 19 (46) (Scheme 8.6). Related reactions have also been reported for diazocyclopropane (47) and diazospiropen-tane (48). 

When the carbopalladation of the bicyclopropylidene is performed in the presence of methyl acrylate, the reaction takes a different course (Scheme 8.34) [79]. The 1,3-diene intermediate 75 reacts in situ with the dienophile to give the spiro[2.5]octane derivative 76. An extension of this cascade Heck-Diels-Alder reaction involving l,3-dicyclopropyl-l,2-propadiene as the alkene partner, an alkenyl or aryl halide and a dienophile has been reported [80]. 

First, following the results of the 1,6-dioxa-spiro[2.5]octane rearrangement (5,19), continuous gas phase conditions were applied in a fixed bed reactor and secondly under liquid phase conditions in a slurry reactor. The catalytic experiments carried out showed that two main reactions took place rearrangement of 18 to the aldehyde 19 and a oxidative decarbonylation reaction to the olefine 1,3,3,4-tetramethyl-cyclohex-l-ene 20, which is assumed to be caused by a formaldehyde elimination reaction. Also observed was a deoxygenation reaction to the alkane 1,1,2,5-tetra-methylcyclohexane 21 (Eq. 15.2.7), explained by elimination of CO. There are several other side-products such as 2,2,3,6-tetramethylcyclohex-l-enyl-methanol, ringcontracting compounds and double bond isomers of dimethyl-isopropylene-cyclopentene. 

Reductive dehalogenation is an efficient method of synthesis of cyclopropanes spiroannulated to five- and higher-membered carbocycles (i.e. compounds in which spiroannulation does not result in accumulation of extra strain) . The required gem-(dihalomethyl)cycloalkanes are usually prepared by halogenation of the precursor diols (equation 1). The cyclization is most efficiently accomplished in the Zn-alcohol-water system . For example, spiro[2.5]octane 7 was prepared in 91% yield using this procedure. This method is useful even for a one-step preparation of bis-spirocyclopropyl compounds as exemplified in equation 2. However, the application of the reductive dehalogenation method to the synthesis of more strained SPC (i.e. spirohexane or spiropentane) often leads to rearranged products. For example, methylenecyclopentane was the only product obtained from bis(bromomethyl)cyclobutane (equation 3) ... 

Diaza-spiro[2,5 octan 1-Alkyl-E16a, 465 (Keton + R — NH2 + H2N-0-S03H]... 

Diaza-spiro 2.5]octan 4-Hydroxy- X/2, 81 (Keton-Derivatis.) X/4, 903 (Kond.)... 

Diaza-spiro[2.5]octan 1-Ethyl-2,4,6-trioxo- E17a, 297 [En-1,1-(C00R)2/Na0H/(H3C)2S(0)I + Harnstoff]... 

Pyridylmethoxy)- -ethylester E16a. 247 (O-Alkyl.) Cyclopenten-l-olat 2-Dimethylami-no-3,4-dioxo-5-dimethyl-iminio-no- E15/2, 1550 (Utnlager.) 5,7-Diaza-spiro 2.5]octan l-Isopropyl-4,6,8-trioxo- E17a, 297 [En — l,l-(COOR)2/NaH/ (H3C)3S(0)I + Harnstoff]... 

Oxa-spiro[4.5]decan VI/3, 533 l-Oxa-spiro[2.5]octan 2,2-Dimethyl-E19d, 865 (Br -> Li/ + Keton) Oxiran 3,3-Diethyl-2-ethenyl-2-methyl- E19d, 880 (Cl —C — C-OLi - Oxiran)... 

H-Pyran 3,4,6,6-Tetramethyl-5,6-dihydro- VI/4, 92 4H-Pyran 2-Methyl-3-propyl-5.6-dihydro- VI/4, 88 Spiro 2.5]octan 1-Hydroxy-1 -methyl- E17b, 1397 (1,1-Br2 -l-OH/l-CHj)... 

Morpholino- E17b, 1598 (7-Succinimido -> 7-H) l-Aza-spiro 2.5 octan l-tert.-Butyl-2-oxo- E16b, 8 (aus Br —CR2 — CO-NH-R)... 

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