Esters, cyclopropyl => conjugated

The photorearrangement of a dienone was noted<4) as early as 1830 in a study of the sesquiterpene a-santonin (1). However, the structure and stereochemistry of the various photoproducts were not conclusively established until 1965.(6) Upon irradiation in neutral media, a-santonin (1) undergoes rapid rearrangement to the cyclopropyl ketone, lumisantonin (2). However, if the irradiation is not terminated after a short period of time the lumisantonin itself rearranges into a linearly conjugated dienone (3). The dienone (3) can be isolated from the photolysis of either (1) or (2) in benzene or ether. In nucleophilic solvents (alcohol or water) the dienone (3) is also photo-chemically active and is further converted into an ester or an acid (photo-santonic acid) (4). 

Addition of the a,3-unsaturated anion (21) to the Michael acceptor (22), in which either alkylation or 1,4-addition is possible, affords only the Michael product. Internal alkylation of the interme ate ester enolates leads to cyclopropyl derivatives (equation 7). Terpenoid polyenes are prepared through conjugate addition of the lithiat protected cyanohydrins (23) to dienyl sulfoxide (24 equation 8). ... 

Conjugate addition to cyclopropyl lactones and fi-keto esters. (4, 219-220). The reaction of the cyclopropyl lactone (1) with 1.5 eq. of dimethylcopper-lithium at -30 to 0° gives the isomeric spirolactones (2) in high yield. The related cyclopropyl /34ceto ester (3) reacts similarly to give (4). 

High enantioselectivities are obtained using N,N,N, N -tetramethyltartaric acid diamide-derived boronate ester 32 in combination with bis(iodomethyl)zinc for asymmetric cyclopropanation of allylic alcohols. Various chiral, non-racemic cyclopropyl-methanols can be obtained in enantiomeric excesses of 91-94%. This methodology has been extended with success to the cyclopropanation of unconjugated and conjugated polyenes and homoallylic alcohols (Equation 47) [45]. 

Lithium phenyl selenolate, LiSePh, is sufficiently nucleophilic to add in conjugate [l,5]-fashion to monoactivated cyclopropyl ketones, nitriles, and esters/ ... 

Acyl azoliums generated from enals have been converted to cyclopropyl carboxylic esters with ee < 99% by reaction with sulfur ylides. Some FLPs have been found to i react by conjugate P/B addition to unsaturated ketones and esters, whereas 1,2-addition to corresponding aldehydes is usual. ... 

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