Cycloadditions iron chloride

Double bonds adjacent to complexed dienes can be cyclopropanated using diazomethane, methyl diazoacetate, or sulfur-based ylids. Cycloheptatriene iron tricarbonyl undergo a [2 -F 2] cycloaddition with chloroketene derived from trichloroacetyl chloride (Scheme 161). 

Catalyst for DIels-Alder reaction of ynamlnes. A zero-valent iron species prepared by reduction of iron(III) chloride with isopropylmagnesium chloride serves as a unique catalyst for cycloaddition of butadiene and ynamines (1) to form 1,4-cyclohexadienamines (2). These products are hydrolyzed by mild acid treatment to (3,y-cyclohexenones (3), which are isomerized to either 4 or 5 by catalytic amounts of rhodium catalysts. 

The main product in the reaction of norbornadiene with buta-1,3-diene resulted from a 1,4-cycloaddition onto the conjugated diene (for extended homo-Diels-Alder reactions, vide infra). On the other hand, the 1,2-homo-Diels-Alder adduct 4 was obtained when bisfcycloocta-tetraenejiron [or iron(III) chloride/isopropylmagnesium chloride] was used as the catalyst. ... 

The use of transition metal complexes as catalysts allows 1,4-cycloadditions to be involved as the major pathway in several cases when conjugated dienes are reacted with norbornadiene. No normal homo-Diels-Alder reaction was observed by reaction of the latter with buta-1,3-diene in the presence of an iron complex catalyst, the main product obtained was such a 1,4-adduct 2f the same adduct 2 was obtained in good yield and selectivity when a catalyst formed from cobalt(II) chloride, diethylaluminum chloride and bis(l,2-diphenylphos-phinojethane was used. ... 

For a few combinations of less reactive dienes and dienophiles, transition metal catalyzed variants of the Diels Alder reaction have been developed. An example is the cycloaddition of an unpolar diene and an unactivated alkyne however, except when the reaction is catalyzed with iron, nickel, cobalt, or rho-dium(I) complexes, the temperature required often causes competing decomposition, even for the intramolecular version. [2] Wilkinson s catalyst [3] - tris(triphenylphosphane)rho-dium(I) chloride - frequently used for hydrogenations and for decarbonylations, permits the cyclization of 4 to the annelated cyclo-hexadiene 5 in excellent yield in only 15 minutes at 55 °C in trifluoroethanol as solvent (Scheme 2). [2c]... 

Cycloaddition reactions of alkynes aided by transition metals were reviewed Various trimerization processes of acetylenic compounds have been reported. Titanium chloride catalyses the trimerization of acetylenic compounds, by way of intermediate complexes that can be isolated and characterized. This is shown in Table 2 for TiCU and 2-butyne. Acetylenes activated by ether groups in the propargyl position undergo trimerization catalysed by NiBri/Mg. Acetylenes without activation also undergo the same reaction, but with lower yields. Iron 7i-complexes can catalyse stepwise polymerization of alkynes ... 

Compared to the relatively young history of the pure metal, aluminium compounds have been known for ages from the above-cited alum class to the more exclusive transition metal-doped aluminium oxides like ruby and sapphire (corundum varieties with chromium for the former and titanium and iron impurities for the latter) or aluminosilicate-like emeralds (a beryl type with chromium and vanadium impurities). However, to the synthetic chemist, aluminium chloride, is de facto one of the first jewels of the aluminium family. Aluminium trichloride (together with titanium tetrachloride, tin tetrachloride and boron trifluoride) is an exemplary Lewis acid that finds many applications in organic synthesis It is extensively used for instance in Friedel-Crafts alkylations and acylations, in Diels-Alder-type cycloadditions and polymerisation reactions. Its involvement in a wide range of reactions has been documented in many reviews and book chapters. ... 

A formal [2+1+1] cycloaddition is achieved by reaction of alkynes with an iron carbonyl species that is prepared in situ from dodecacarbonyltriiron Fe3(CO)i2 in the presence of certain amines. This procedure provides cyclobutenediones in moderate to good yields after demetalation with copper(II) chloride (Scheme 4-14). Instead of amines and dodecacarbonyltriiron, alkoxides such as ter/-BuOK can be reacted with pentacarbonyliron to give reactive carbonyliron intermediates that undergo cyclization... 

Addition of an T -allyl-Fp complex to this compound affords an T -aIlyl-Fp-substituted cycloheptatriene system. Two double bonds are involved in an (T -diene)iron complex. The remaining free double bond of the silyl enol ether attacks as a nucleophile at the cationic r -alkene-Fp moiety to form an (Tj -diene)iron complexed cyclopentane annulated cycloheptadienone. Treatment with CAN in methanol under carbon monoxide atmosphere releases the methoxycarbonyl-substituted free ligand (Scheme 4-25). Reaction of the Ti -dienyliumiron intermediate of Scheme 4-25 with an ( , Z)-isomeric mixture of ri -crotyl-Fp proceeds with high diastereoselectivity. Four new stereogenic centers are formed in the course of this formal [3+2] cycloaddition. A hetero [3+2] cycloaddition is also feasible between T -ailyl-Fp complexes and aromatic aldehydes in the presence of zinc chloride or titanium(IV) chloride to provide tetrahydrofuran derivatives (Scheme 4-26). A 1,2-shift of the iron complex fragment occurs in the course of this reaction. Employment of imines affords the corresponding pyrrolidines. ... 

A [4+2] cycloaddition of butadiene with 2-butyne or diphenylacetylene catalyzed by either (dicyclooctatetraene)iron(O) [Fe(cot)2], a combination of iron(III) chloride and isopropylmagnesium chloride, or tris(acetylacetonato)iron and triethylaluminum provides... 

The methodologies described could not be applied to the synthesis of un-symmetrical and some fluoro-substituted HBCs. Therefore an alternative method was developed as shown in Scheme 4.35 [200, 201], It involves [4 + 2] Diels-Alder cycloaddition of a suitably substituted diphenyl acetylene 172 and 2,3,4,5-tetrarylcyclopenta-2,4-dien-l-one 171. The cyclopentadienone is synthesized via double Knovenagel condensation between a 4,4 -substituted benzyl 169 and 1,3-diarylacetone 170, see Scheme 4.35. Oxidative cyclodehydrogenation of 173 with iron (HI) chloride yields HBC derivatives 174. Thus both unsymmedical and symmetrical HBC derivatives can be obtained via this versatile route. 

---