Stereochemistry of intramolecular cyclopropanation of an organoiron reagent

Abstract

Supplementary Material Available: Representative experimental procedures for the major transformations shown and characterization data for all new substances (7 pages). Ordering information is given on any current masthead page. 2.7 (C6H6) 12

Cyclopropanes from reactions of transition metal carbene complexes with olefins

“…The instability of the higher alkylcarbene complexes relative to the methylcarbene complexes also explains the lack of efficient transfer methods for the higher alkylcarbene complexes although low transfer yields have been achieved with Cp(CO)(PPh3)Fe= CHCH2CH3+ 22 and entropically favored intramolecular transfers are feasible. 29,30 In the case of the dimethylcarbene complexes Cp-(CO)(L)Fe=C(CH3)2+ (L = CO, PPh3), hydride migration is relatively slow to yield Cp(CO)(L)Fe(CH2= CHCH3)+; however, the increased bulk and decreased electrophilicity at CQ also inhibit the transfer reaction to such an extent that hydride migration is still a competitive side reaction.22®'0 C. Results of Transfer Experiments Table I is an extensive summary of the reactions of electrophilic transition metal carbene complexes with olefins which yield cyclopropanes. The table is organized generally according to the structure of the carbene moiety transferred and not according to metal or olefin used.…”

Organoiron Compounds for Selective Organic Transformations

“…For the straightforward cyclopropanation of alkenes, Helquist et al developed crystalline sulfonium salts, such as 120 (Scheme 38). [74][75][76] Compound 120a is obtained from the sodium ferrate 2 and chloromethyl methyl sulfide in a two-step synthesis on large scale. The complex 119b, isolated in 93% yield after crystallization, is subsequently alkylated with dimethoxycarbenium tetrafluoroborate to furnish the sulfonium salt 120a in about 55% yield.…”

Fe Organoiron Compounds Part B13

“…On the basis of all these results the cyclopropanation reactions are assumed to proceed via the carbene derivatives [Fp=C(R1)CH a ]X. Intramolecular cyclopropanation with formation of norcarane takes place by treatment of FpCH=CH(CH2)aCH=CH2 in CH2C~ with HBF 4 at -50"C for 1 hand then with aqueous NaHCO a [174], see also [198,199], or of FpCH(SC6Hs)(CH2)4CH=CH2 with [0(CH a h]BF 4 in CH 2 Cl 2 [199].…”

“…9) has been prepared from 1-iodohepta-1,6-diene with 2 moLe LiC 4 Hg-t foUowed by 1 moLe Fpl [174], see aLso [199]. 9) has been prepared from 1-iodohepta-1,6-diene with 2 moLe LiC 4 Hg-t foUowed by 1 moLe Fpl [174], see aLso [199].…”