HIGHLY FUNCTIONALIZED VINYLCYCLOPROPANE DERIVATIVES BY REGIOSELECTIVE AND STEREOSELECTIVE REACTIONS OF FISCHER CARBENE COMPLEXES WITH 1,4-DISUBSTITUTED ELECTRON-DEFICIENT 1,3-DIENES

The thermal reaction of Fischer carbene complex 1 with electron-deficient 1,3-dienes such as methyl (E,E)-2,4-hexadienoate (2) provided functionalized vinylcyclopropanes like 3 in good yields. Similar results were obtained by employing related unsaturated esters 4,17, and 21 or nitrile 6. The periselectivity as well as regioselectivity of these carbene-transfer reactions are generally very high, and the diastereomer with the methoxy group cis-positioned with respect to the olefinic moiety is largely favoured (> 85:15). A mechanistic rationale of these observations is given. Double adducts were only formed as minor sideproducts in these reactions, but by employing amide 13 as electron-deficient diene they were very easily formed with 1. The [2 + 1] cycloaddition could also be extended to methylcarbene complex 24 and diene 2, but the corresponding vinylcyclopropane 25a was so far only obtained in low yield.