Synthesis via oxazolines - one carbon homologation of aldehydes and ketones to thiiranes and olefins

✍ Scribed by A.I. Meyers; Michael E. Ford

• Publisher: Elsevier Science
• Year: 1975
• Tongue: French
• Weight: 166 KB
• Volume: 16
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)75015-5

✦ Synopsis

_ Thiiranes are useful precursors for the synthesis of olefins by phosphlne la or phosphltelb'c mediated desulfurizations. However, these heterocycles are obtained from multi-step procedures involving intermediate oxiranes2 derived from carbonyl compounds or olefins. The synthetic utility of oxazollnes has been amply demonstrated3 and we now report a route to thliranes and olefins using this readily available heterocycle. Recently! the lithlo salt of several 2-(propargylthio)-2-thlazolines lwas condensed with benzaldehyde providing the corresponding 2-prob\argyl-3_phenylthllranes, however, the modest yields (-20%) encountered appear to have dlscoura$ed further study. Our extensive studies on oxazollnes have led us to the P-(thlomethyl)-210xaQoline5 2 which was found to readily metalate with n-butyllithlum (THF, -78") and may be S 0 R-CaC-CH2S \ -(> CH3S \ <k Me N N Me l_, R=H, Ph 2 alkylated with various carbonyl compounds furnishing, ln a single operation, the homologated thilranes in 61-78% yields (Table I).6 Reaction proceeds by rapid addition of the lithlo oxazolines 3 to the carbonyl compound producing 4_, which was trapped as its trimethylsllyl ether 5 at -78". However, if the solution of Qwas allowed to slowly warm to ambient, rearrangement If the alkyl group on sulfur is other than methyl, benzyl, cyanomethyl, or carboethoxymethyl (i.e. ethyl, c-propyl, n-butyl, etc.), the lithio salt could not be generated even though a wide variety of bases, solvents, and temperatures were examined.