5-lactone complexity

There appear to be few examples of the formation of azetidin-2-ones by closure of the C(2) —C(3) bond. One reaction which fits into this category involves reaction of the iron carbonyl lactone complexes (144) with an amine to give the allyl complexes (145) which on oxidation are converted in high yield to 3-vinyl-/3-lactams (146) (80CC297). 

Ford, L., et al., 1974. Cry.stal. structure of a ly.sozyme-tetra.saccharide lactone complex. y(9wm z/ of Molecular Biology 88 349-371. 

Titanium(IV) chloride is used as the catalyst in a Knoevenagel reaction between various 2,2-disubstituted 3-hydroxypropanals and malonic acid or its esters. The products are substituted dihydropyran-2-ones (536) (79LA751). The reaction, which occurs cleanly and in good yield, utilizes an excess of the titanium halide and is thought to involve a cyclic complex which undergoes an ester exchange to a lactone complex (Scheme 198). 

Reactions between halogenoalkynes and the lactone complexes (34) afford a series of binuclear orange-red //-vinylidene derivatives (35) (62) ... 

Cationic t 3-allyltetracarbonyliron complexes are generated by oxidative addition of allyl iodide to pentacarbonyliron followed by removal of the iodide ligand with AgBF4 under a carbon monoxide atmosphere [35]. Similarly, photolysis of vinyl epoxides or cyclic vinyl sulfites with pentacarbonyliron or nonacarbonyldiiron provides Jt-allyltricarbonyliron lactone complexes. Oxidation with CAN provides by demetallation with concomitant coupling of the iron acyl carbon to one of the termini of the coordinated allyl moiety either [3- or 8-lactones (Scheme 1.12) [36, 37]. In a related procedure, the corresponding Jt-allyltricarbonyliron lactam complexes lead to P- and 8-lactams [37]. 

Under more severe conditions of temperature and pressure, the complexes Co2(CO)e(RC2R ) react with carbon monoxide according to Eq. (19) to give lactone derivatives 19, 24). Lactone complexes have been... 

A mechanism for the formation of lactone complexes from Co2(CO)g-(RCgR ) has been proposed (Scheme 1) 58)] it is based on studies of the... 

Few chemical reactions of lactone-carbonylcobalt complexes have been reported. Hydrogenation 24) of butenolactone-heptacarbonyldi-cobalt, Co2(CO)g(HC2H), gives y-butyrolactone, butyric acid, and dodecacarbonyltetracobalt. Treatment of the same lactone complex with sulfuric acid in warm acetone 50, 125) gives a cobalt cluster compound of formula Co3(CO)gCCH=CHCOOH. The use of methyl alcohol in place of acetone in the latter reaction yields Cog(CO)gCCH=CHCOOMe. 

Work in this area has also focused on optically active complexes. Exchange of vinyl ether complex (94) with optically active alcohols gives unequal mixtures of diastereomeric vinyl ether complexes in the best case, (-)-menthol gives a 4 1 mixture emiched in (99). Optically active epoxides are capable of affording enantiomerically pure complexes allylic alcohol substituents allow reversible conversion to the related lactone complexes (100) (equation 21). 

The chemistry of this class of complexes is dominated by the 7r-allyliron tricarbonyl lactone complexes (155), which have been studied extensively and reviewed. Compounds (155) are normally prepared by reaction of vinyl epoxides with a source of Fe(CO)4 , such as (1) and photolysis, (2) and heat, or (2) in Tetrahydrofinan (THF) or with ultrasonication (see Sonication) the latter two methods are considered to be superior. It has been reported that butene-1,4-diols, particularly the cis isomers, (with or without Lewis acids), 3-butene-1,2-diol sulfites, 3,6-dihydrooxazmes, or related compounds also give (155) with (2). The complexes are isolated as anti isomers at C-1. Substituents at C-3 are oriented syn when not constrained in a ring, whereas... 

A number of enantiomerically pure complexes have been made, and this chemistry has been used in several natural product syntheses. Enantiopure complexes are readily available from the corresponding vinylic epoxides, and in cases where diastereoselective complexation is possible, diastereoselectivities tend to be moderate (typically 3 1 -4 1). The rationale for the origin of this diastereoselectivity has been proposed to derive from a preferential complexation of a Fe(CO)4 fragment to the alkene anti to the epoxide. Since the initial vinyl epoxide is conformationally flexible, four diastereomeric itt-complexes would be produced as a consequence of anti or syn complexation to the s-trans or s-cis conformers. Isomerization of these initial 7r-complexes to alkoxy- 7r-allyl species would then enable interception of an iron-bound carbonyl ligand by the alkoxide to afford diastereomeric lactone complexes. Fortunately, equilibria between the two possible trans itt-allyl complexes and their more stable cis Tr-aUyl analogs simplifies the outcome significantly. Thus, for trans vinyl epoxides, the major diastereomer typically is the one designated as endo cis (the C-1 substituent points toward the iron atom) the minor diastereomer corresponds to the exo cis isomer (the C-1 substituent points away from the iron atom) (Scheme 51). For cis vinyl epoxides, this outcome is reversed - the exo cis isomer is the major product. 

Bates, R. W., Fernandez-Megia, E., Ley, S. V., Ruck-Braun, K., Tilbrook, D. M. G. Total synthesis of the cholesterol biosynthesis inhibitor 1233A via a (jc-allyl)tricarbonyliron lactone complex. J. Chem. Soc., Perkin Trans. 11999,1917-1925. 

The TiCLrmediated Mukaiyama aldol reactions between 7r-allyltricarbonyliron lactone complexes and chiral aldehydes were well documented by Ley and coworkers [37]. (/ )-Trimethylsilyl enol ether 23 (>96% ee) was prepared from the methyl ketone complex 22 by treatment with MesSiOTf/EtsN in CH2CI2 and this was then reacted with (R)- and (5)-2-benzyloxypropanal 24 under the influence of TiCl4 in CH2CI2 at -78 °C. Although the reactions proceeded very slowly and apparent hydrolysis of the silyl enol ether occurred, the aldol products 25 and 26 were isolated in excellent diastereoselectivity in both cases (Scheme 1-8). Interest-... 

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