Butyrolactone spiro, formation

Homoenolate Reactivity The ability to generate homoenolates from enals and its application to the preparation of y-butyrolactones 30, through reaction with an aldehyde or aryl trifluoromethyl ketone, was reported independently by Glorius [8], and Bode and Burstein [9] (Scheme 12.4). A sterically demanding NHC catalyst is required to promote reactivity at the d terminus and to prevent competitive benzoin dimerisation. Nair and co-workers have reported a similar spiro-y-lactone formation reaction using cyclic 1,2-diones, including cyclohexane-1,2-dione and substituted isatin derivatives [10]. 

A similar spiro-fused starting material was prepared to study the thermolysis of a 1,3-dioxane analog. As found for the dithia compound (cf. Section 8.11.6.3.1), a carbene-derived dimer was formed as the major detectible product (20%) <2002TL1927>. Other products, such as tricycle 185, have been identified in subsequent studies <2004CJC1769>. However, phenyl substitution at G-4 provided completely different thermolysis products, probably via formation of an open-chain bis-radical. Thus, 3-phenyl-7-butyrolactone and, after CO2 extrusion, phenylcyclo-propane are the major reaction products (Scheme 58) <2002CJC1187>. 

Miscellaneoas Reactions.—Little interest has been shown this year in the photochemistry of alkyl nitrites. Irradiation of the acetylenic nitrite (230) 1 to the formation in poor yield of y-butyrolactone (231). A mechanism involving cyclization of the alkoxy-radical, followed by formation of the spiro-intermediate (232), is shown in Scheme 18. The intramolecular addition of thiiyl radical to... 

Figueredo and coworkers were driven by the total synthesis of a polycyclic natural molecule (the putative structure of stemonidine) [22] when they reported their Reformatsky-type reaction for the diastereoselective construction of spiro-a-methylene-y-butyrolactone 48. Reaction of the starting ketone 47 with ethyl bromomethylacrylate and zinc led to the formation of the desired spirolactone 48 in 86% yield and with complete facial selectivity (Scheme 9.13). 

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