Bicyclic cyclopropanols

Asymmetric cyclopropanol formation has been achieved with olefmic acylsulfonamides, which act like olefmic esters. Thus, their reaction with 1 provides a method for synthesizing cyclopropanols in an optically active form. As represented by Eq. 9.41, alkylation of Oppolzer s camphor sultam and reaction of the resulting unsaturated acylsulfonamides with 1 provides optically active bicyclic cyclopropanols having exclusively the structure shown in the equation [76],... 

Sato et al. developed an interesting enantioselective synthesis of bicyclic cyclopropanols 37 from N-acylcamphorsultam derivatives 36. Products with enantiomeric excesses of up to 98% were obtained (Scheme 11.11) [102]. 

Bridgehead bicyclic cyclopropanols or cyclopropyl silyl ethers 103 (R=H) cleaved to ring-expanded mixtures of cyclic (1-hydroxy ketones 105 and (1-diketones 106 in good overall yields catalyzed by 10 mol% of VO(acac)2 in the presence of oxygen (Fig. 32) [191, 192]. With 3-substituted substrates 103 (R=Me), mixtures of bicyclic endoperoxide hemiketals 104B and (1-hydroxy ketones 105 arose. In separate experiments it was shown that 105 is not oxidized to 106 under the reaction conditions, and thus the products most likely form from... 

Fig. 32 Vanadyl acetylacetonate-catalyzed oxidative ring expansion of bicyclic cyclopropanols...

Cyclic chiral end ethers 7.136 generated from acetals of chiral diols react selectively with the Simmons-Smith reagent or with CT /E Zn. After removal of the chiral auxiliary by oxidation and base treatment, bicyclic cyclopropanols 7.137 are obtained with an excellent enantiomeric excess [213, 1490, 1491, 1492] (figure 7.83). The methylene group is introduced on the face of the double bond opposite to that of the i-Pr group next to the OH of the chiral auxiliary. 

Hydrogenolysis of bicyclic cyclopropanol 35 over Pd/C produced cyclohexanone 36 with excellent diastereospecificity (Scheme 2.33) [50]. 

Iwasawa, N. Funahashi, M. Hayakawa, S. Ikeno, T. Narasaka, K. Synthesis of mediumsized bicyclic compounds by intramolecular cyclization of cyclic /i-keto radicals generated from cyclopropanols using Mn(III) tris(pyri-dine-2-carboxylate) and its application to total synthesis of 10-isothiocyanatoguaia-6-ene. 

However, reaction with a solution of / -toluenesulfonic acid in refluxing benzene for one hour or with methanolic potassium hydroxide at room temperature for three hours did not produce the expected bicyclic ketones from simple ring cleavage of the cyclopropanol moiety of 1, but instead the tra 5-l,6-dimethylbicyclo[4.3.0]nona-2,7-dione (2) was formed in 60% yield. A cyclopropoxide isomerization was considered to be involved to rationalize this rearrangement. ... 

Cyclic a -nucleofuge-a,)S-unsaturated ketones 35 (X = Cl, Br, OMs) similarly condensed with dimethyl sodiomalonate but the yields of cyclopropanols were poorer (14-20%). The cyclopropanols 36 were obtained as mixtures of diastereomers, which were accompanied by bicyclic y-lactones 37 in 15-22% yield. ° ... 

The Amberlyst-15 catalyzed ring opening of cyclopropanols occurs at room temperature. During the reaction of 9 epimerization produces trans- Q as a side product. The mode of ring opening is site selective at the peripheral methylene carbon for bicyclic siloxycyclopropanes. Steric factors may influence the selectivity. 

Addition of phenylselanyl bromide, in the presence of triethylamine, to a bicyclic vinyl-cyclopropanol 16 resulted in an electrophilically initiated ring expansion to the corresponding spirocyclobutanone 17 with high diastereomeric purity. This rearrangement forms the basis of the total synthesis of plumericin. 

Functionalized cyclopropanes. The reductive coupling of esters with 1-alkenes by a Grignard reagent and titanium alkoxide gives rise to cyclopropanols (the Kulinkovich reaction). With the use of ethylene carbonate, the condensation gives rise to 2-substituted cyclopropanone hemiacetals. An intramolecular version delivers bicyclic products. ... 

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