Lactone ring expansion

Lactone ring expansion.1 The 7-lactone 2 can be expanded to the protected y-lactol 4, characteristic of mevinic acids, by reaction of the lactol of 2 with this Wittig reagent to provide a vinyl sulfide 3. Conversion of the vinyl sulfide to 4 was... 

Lactone ring expansion. The lithio derivative from this sulfoxide (LDA) reacts with lactones to form adducts which on further treatment with KH and then r-BuLi are transformed into ketenes. Acidification regenerates lactones of one size larger. This reaction sequence works well for expansion of 5- and 6-membered lactones. For the synthesis of macrolides, it is necessary to quench the ketene with pyridine-2-thiol and use the Corey-Nicolaou method to effect reclosure of the lactone ring. 

Cyclic ketones react through ring expansion to yield lactones (cyclic esters). For example cyclopentanone 7 can be converted to 3-valerolactone 8 ... 

Reaction between lactones and ammonia or amines ring expansion of lactams... 

The ring expansion of cyclobutane derivatives to other carbocycles remains to be one of the most powerful tool in synthetic organic chemistry. Cyclobutanones are exceptionally facile starting materials for the preparations of y-lactones as well as cyclopentanones. 

Lactones by ring expansion of lactols. Medium-sized lactones can be obtained in reasonable yield by photolysis of the hypoiodites of catacondensed lactols, which results in regioselective cleavage of the bridging bond. The substrates are available by the general route shown for the 6/6 lactol 1, which is cleaved to the 10-membered lactone 2. This cleavage can be used for preparation of 9-membered... 

The ring-expansion carbonylation of epoxides is the most widely studied field in the epoxide carbonylation chemistry since the product lactones are highly attractive targets particularly, /1-lactones are useful compounds due to their versatility in organic synthesis [ 14,15] as well as their utilization as monomers to produce poly(3-hydroxyalkanoate)s, naturally occurring biodegradable polyesters [16-19]. 

The first successful example of a catalytic ring-expansion carbonylation was reported by Aumann et al. in 1970s [20,21], Here, isoprene oxide was allowed to react with CO in the presence of [Rh(cod)Cl]2 to give an fi,y-unsaturated lactone (Scheme 2). Soon after their report, the carbonylation of styrene oxide to yield the corresponding /1-lactone was demonstrated by using RhCl(CO)(PPh3)2 [22], The scope of this method is, however, quite... 

Poly(3-hydroxyalkanoate)s have potential for application to engineering plastics endowed with biodegradable nature. One of the synthetic approaches to the polyesters is the ring-opening polymerization of -substituted /3-lactones which can be effectively produced by ring-expansion carbonylation of epox-... 

Silyloxypropanols (314) derived from lactones undergo oxidative ring expansion to afford higher homologous o ,/3-unsaturated lactones (316) (90TL197). The reaction proceeds through the fluoride ion assisted formation of intermediate 315, which on reductive elimination of F " species yields the product (Scheme 80). 

The opened epoxide shown in Fig. 15 is also an intermediate in the catalytic ring expansion of epoxides to p-lactones (see Sect. 8.4). In this context, Drent and coworkers patented a catalytic system of dicobaltoctacarbonyl Co2(CO)g and... 

Fig. 40 Synthesis of cyclic poly((3-lactone) by metal-free ring-expansion polymerization...

Kudoh R, Sudo A, Endo T (2009) Synthesis of eight-membered lactone having tertiary amine moiety by ring-expansion reaction of 1,3-benzoxazine and its anionic ring-opening polymerization behavior. Macromolecules 42 2327-2329... 

Kricheldorf HR, Fechner B (2002) Polylactones. 59. Biodegradable networks via ring-expansion polymerization of lactones and lactides. Biomacromolecules 3 691-695... 

Kricheldorf HR, Lee S-R, Schittenhehn N (1998) Macrocyclic polymerization of (thio) lactones - stepwise ring expansion contraction. Macromol Chem Phys 199 273-282... 

Jeong W, Hedrick JL, Waymouth RM (2007) Organic spirocyclic initiators for the ring-expansion polymerization of P-lactones. J Am Chem Soc 129 8414-8415... 

A recent approach to the papulacandin spiroketal features an elegant pinacol-type ring expansion of lactone 11 as shown in Equation (2) <1999T15159>. 

Ring expansion of thiono lactones (cyclic ethers)... 

A novel entry to decahydrocyclopentacyclooctene derivatives via the intramolecular photocycloaddition of fused a,/3-unsaturated y-lactones has been developed (80CC1011). Irradiation of the butenolide (153) in acetone solution gave both the fused and bridged photoadducts (154) and (155) (2-3 1). The major adduct was hydrolyzed, oxidized and esterified to afford (156). Reductive cleavage of the unsaturated keto ester (156) with lithium in ammonia afforded a five-component mixture of a,/3- and /3,y-unsaturated esters. Equilibration with 0.1M sodium methoxide in methanol converted the mixture into a single a,j8-unsaturated ester (157 Scheme 34). This annelative two-carbon ring expansion method may find application in the synthesis of ophiobolin and ceroplastol sesterterpenes. 

The key steps in the ring expansion of the cyclobutanones (186) and (787) are the Baeyer-Villiger oxidation effected by H202—HOAc. It is noteworthy to point out that the Baeyer-Villiger oxidation is regiospecific and serves to be an excellent method for the preparation of y-lactone from cyclobutanones. 

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