Intermolecular reactions of new halovinylcarbenes - versatile synthesis of (halovinyl) cyclopropanes

Deprotonation of the oligohalopropenes 1A, 1B, 1C with LiTMP or LiHMDS in the presence of olefins 3 led to halovinylcyclopropanes 4A, 4B, 4C by intermolecular trapping of the corresponding halovinylcarbenes. Mixtures 4B/4C and (dichloroethenylidene) cyclopropanes 5 can be obtained from 1,1,2,3,3-pentachloropropane (6), LiHMDS and olefins 3.     

Conformational behaviour of 3-phenyl- and 3-carbomethoxy-substituted cyclopropene derivatives

According to MNDO calculated heats of formation for various 3-substituted cyclopropenes the π-acceptor methoxycarbonyl as well as the π-donor group phenyl both prefer a non-bisected orientation with respect to the three-membered ring. Temperature dependent NMR chemical shifts seem to confirm this behaviour for the free molecules. In the crystalline state, however, 1,2,3-triphenylcyclopropene (3e) and 3-isopropyl-1,2,3-triphenylcyclopropene (3f) both adopt a conformation with a bisected orientation of the 3-phenyl groups.     

Convenient syntheses of dichloroethenylidenecyclopropanes: Precursors to difunctional cyclopropane derivatives

Dichloroethenylidenecyclopropanes 4 are obtained in good yields from olefins and tetrachloropropenes 1 and 3 or, more conveniently pentachloropropane 7. The highly reactive allenes 4 readily add nucleophiles (such as methoxide) as well as electrophiles.