.alpha.-Methylene .beta.-lactones as masked allenes and allene equivalents: some selected chemical transformations
摘要:
Selective chemical transformations have been performed on a number of alpha-methylene beta-lactones to illustrate that these highly functionalized heterocycles serve as useful building blocks in organic synthesis. Thus, thermal decarboxylation of these ''masked allenes'' provides a useful regioselective preparation of allenes with a predetermined substitution pattern. Nucleophilic addition takes place at the carbonyl group with ring opening, but free-radical addition, e.g., thiophenol, and electrophilic addition, e.g., bromine, proceed at the exomethylene group with preservation of the beta-lactone ring. [4 + 2] Cycloaddition with cyclopentadiene affords the expected beta-lactones, which on thermal decarboxylation lead to 2-alkylidenenorbornenes. This regio- and stereoselective transformation establishes the alpha-methylene beta-lactones as valuable allene equivalents. The alpha-methylene beta-lactones serve also as dipolarophiles by undergoing readily 1,3-dipolar cycloaddition with diazoalkanes. Reaction with Lawesson's reagent affords a hitherto unknown alpha-methylene beta-(S)-lactone.
α-Methylene-β-lactones as novel allene equivalents: regioselective [4+2] cycloaddition and stereoselective decarboxylation for the introduction of exo-alkylidene functionalities
作者:Waldemar Adam、Ludwig Hasemann
DOI:10.1016/0040-4039(91)85032-z
日期:1991.11
β-Lactone-capped allene dienophiles afforded with cyclopentadiene spiro-β-lactone as [4+2] cycloadducts, which on thermal decarboxylation gave regio- and stereoselectively E-5-alkylidene 2-norbornenes.
.alpha.-Methylene .beta.-lactones as masked allenes and allene equivalents: some selected chemical transformations
作者:Waldemar Adam、Rainer Albert、Ludwig Hasemann、Victor O. Nava Salgado、Bernd Nestler、Eva Maria Peters、Karl Peters、Frank Prechtl、Hans Georg Von Schnering
DOI:10.1021/jo00020a017
日期:1991.9
Selective chemical transformations have been performed on a number of alpha-methylene beta-lactones to illustrate that these highly functionalized heterocycles serve as useful building blocks in organic synthesis. Thus, thermal decarboxylation of these ''masked allenes'' provides a useful regioselective preparation of allenes with a predetermined substitution pattern. Nucleophilic addition takes place at the carbonyl group with ring opening, but free-radical addition, e.g., thiophenol, and electrophilic addition, e.g., bromine, proceed at the exomethylene group with preservation of the beta-lactone ring. [4 + 2] Cycloaddition with cyclopentadiene affords the expected beta-lactones, which on thermal decarboxylation lead to 2-alkylidenenorbornenes. This regio- and stereoselective transformation establishes the alpha-methylene beta-lactones as valuable allene equivalents. The alpha-methylene beta-lactones serve also as dipolarophiles by undergoing readily 1,3-dipolar cycloaddition with diazoalkanes. Reaction with Lawesson's reagent affords a hitherto unknown alpha-methylene beta-(S)-lactone.