Lactonization/benzylic

Allyl silanes react with epoxides, in the presence of Bp3-OEt2 to give 2-allyl alcohols. The reaction of a-bromo lactones and CH2=CHCH2Si SiMe3)3 and AIBN leads to the a-allyl lactone. " Benzyl silanes coupled with allyl silanes to give ArCH2—R derivatives in the presence of VO(OEt)Cl2 " and allyltin compounds couple with allyl silanes in the presence of SnCU. " Allyl silanes couple to the a-carbon of amines under photolysis conditions. ... 

The efficient stereocontrol observed in the benzylic lactone hydro-genolyses described in the section on Lactonization/Benzylic Lactone Reduction prompted an investigation into methods for preparing analogous fused bicyclic lactones from enamides 89, 92, 94, and 96. The possible intermediacy of benzylic carbocation 123 in the triethylsilane... 

N-(Benzyloxycarbonyl)-L-serine p-lactone Serine, N-carisoxy-, p-lactone, benzyl ester, L- (9) (26054-60-4)... 

Kalvoda, L. et at, Coll Czech. Chem. Comm., 1976, 41, 800 D-lactone tribenzoyl Me ester) Prystai, M. et al, Coll Czech. Chem. Comm., 1976, 41, 1426 D-lactone benzyl benzoyl Me ester)... 

PCL catalysed the enzymatic copolymerisation of P-PL with e-CL in bulk at 60 °C. Low MW (Mn = 520) polyesters were produced. Ring-opening copolymerisation of another four-membered lactone, benzyl malolactanate (BML), was enhanced, based on yield and MW, through the addition of small amounts of P-PL. BML was polymerised in the presence of 17 mol% P-PL at 60 °C for 24 h. 

Quintard and Alexakis developed a double Michael addition reaction of enals, taking advantage of the high reactivity of vinyl sulfone-initiated nucleophilic addition of benzaldoxime, triazole, Angelica lactone, benzyl mercaptan, and 174. The powerful organocascade allows for the rapid construction of highly attractive synthons in high enantioselectivities (typically, 99% ee) [117]. 

Of the 11 compounds which constitute approximately 86% of jasmin volatiles, only benzyl acetate, i7t-jasmone (18), and methyl jasmonate possess the characteristic odor of jasmin. Trace components including i7t-j asrnin lactone [34686-71-0] (20) (0.9%) andmethyl ( /-jasmonate (6) (0.1%) are the key contributors to the jasmin odor. 

It is important to note that the one-step conversion of 27 to 28 (Scheme 4) not only facilitates purification, but also allows differentiation of the two carbonyl groups. After hydrogenolysis of the iV-benzyl group (see 28—>29), solvolysis of the -lactone-ring in 29 with benzyl alcohol and a catalytic amount of acetic acid at 70 °C provides a 3 1 equilibrium mixture of acyclic ester 30 and starting lactone 29. Compound 30 can be obtained in pure form simply by washing the solid mixture with isopropanol the material in the filtrate can be resubjected to the solvolysis reaction. 

Zinc bromide promoted addition of a functionalized benzyl Grignard reagent to the a,/ -unsat-urated y-lactone, 3-(4-methylphenylsulfinyl)-2(5//)-furanone, via a zinc-chelated intermediate, gave, after several synthetic steps, (-)-podorhizon with 95% ee18. 

Zur Reduktion von 4-Oxo-l-benzyl-3-athoxycarbonyl-pyrrolidin s.S. 217. Oxo-lactone werden am besten mit Zinkboranat selektivzu Hydroxy-lactonen re-duziert4,5 mit Natriumboranat wird zusatzlich die Lacton-Gruppe reduktiv gespalten z.B.4 ... 

Asymmetric alcoholyses catalyzed by lipases have been employed for the resolution of lactones with high enantioselectivity. The racemic P-lactone (oxetan-2-one) illustrated in Figure 6.21 was resolved by a lipase-catalyzed alcoholysis to give the corresponding (2S,3 S)-hydroxy benzyl ester and the remaining (3R,4R)-lactone [68]. Tropic acid lactone was resolved by a similar procedure [69]. These reactions are promoted by releasing the strain in the four-membered ring. 

Rhodium catalysts have also been used. Benzylic halides were converted to carboxylic esters with CO in the presence of a rhodium complex. In this case, the R could come from an ether R20, a borate ester B(OR )3, or an Al, Ti, or Zr alkoxide. Reaction with an a,co-diiodide, BU4NF and Mo(CO)e gave the corresponding lactone. ... 

Secondary alcohols such as cyclohexanol or 2-butanol also react on heating for 20-120 min at 80 °C with TCS 14 in the presence of BiCl3 to give the chloro compounds cyclohexyl chloride 784 and 2-chlorobutane in 93 and 90% yield, respectively, HCl, and HMDSO 7 [11, 12]. Benzyl alcohol is transformed likewise by Me3SiCl 14 after 120 min. at 80 °C into benzyl chloride in quantitative yield. Analogously, esters such as 2-acetoxypropane 785 are also converted by TCS 14 in 100% yield into chloro compounds such as 786 and trimethylsilyl acetate 142. The yS-lactone 787 gives rise to 788... 

Bromomethyl-3,4-dibromo-3,4-dihydrocoumarin 1 (Fig. 11.4) and its chloro-methylated analogue 2b rapidly and progressively inactivate a-chymotrypsin and also the activities of a series of trypsin-like proteases. A benzyl substituent characteristic of good substrates of a-chymotrypsin was introduced at the 3-position to make inhibition more selective. This substituted dihydrocoumarin 3 irreversibly inhibited a-chymotrypsin and other proteases. These functionalized six-membered aromatic lactones, and their five- and seven-membered counterparts, 3//-benzofuran-2-ones 2a26 and 4,5-dihydro-3//-benzo[b]oxepin-2-ones 2c,27 were the first efficient suicide inhibitors of serine proteases. Their postulated mechanism of action is shown in Scheme 11.2. 

Nicolle, J.-P. Hamon, J.-F. Wakselman, M. Lactones phenoliques halomethylees, inhibiteurs bifonctionnels de proteases IV. Preparation de derives chloromethyles de la dihydro-3,4-benzyl-3-coumarine et de la tetrahydro-2,3,4,5-benzoxepinone-2. Bull. Soc. Chim. Fr. 1977, 83-88. 

Ci4HlfiOe Methyl 2-C-benzyl-a-L-xi/Zo-3-hexulo-3,6-furanosidono-l,4-lactone BKHXLA 37 393... 

Steric hindrances may also be the reason why quaternary salts of 8-alkylnarcotoline (130) were transformed during Hofmann degradation to analogous keto acids (131) (111,112) and not to the enol lactones (Scheme 24). In some cases (5,87) the keto acids and their esters have been synthesized from the corresponding enol lactones by hydration (Section III,A,2). Nornarceine (107) was prepared from JV-benzyl-(—)-a-narcotinium bromide (139, X = Br) by Hofmann degradation followed by N-debenzylation and ester hydrolysis (109). 

Lactones (cyclic esters) are usually stable toward hydrogenolysis. However, the aromatic lactones contain benzylic C—O bonds and can be hydrogenolyzed. As an example, the hydrogenolysis of an aromatic lactone was performed over Ra-Ni in THF under 4 atm H2 pressure at 50°C for 30 hours.213... 

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