2-Furanone ring with rearrangement

Furan as solvent in Grignard reactions 16, 679 2-Furanone ring with rearrangement 16, 764 2-Furanones... 

Sodium methoxide 2>Furanone ring with rearrangement... 

Irradiation of the furanone derivative (77a) affords the two products (78) and (79) shown in Scheme 5. When the oxygen function at C-2 is not methylated (77b), irradiation yields the products (80, 81) (Scheme 6). In this case a different rearrangement mechanism is permitted as a result of the relative ease of opening of the furanone ring. The route to product (80) is thought to involve a Norrish Type II process of the carbonyl group with the proximate methoxy function. Subsequent rearrangement via the spiro intermediate (82) ultimately provides the product (80). In the first example (Scheme 5) the formation of (78) also involves... 

Reactions of4-hydroxy-2-cyclobutenones 364 with (diacetoxyiodo)benzene in 1,2-dichioroethane at reflux afford 5-acetoxy-2(5//)-furanones 365 as rearranged products (Scheme 3.146) [466], The formation of these products is explained by ring cleavage in the hypervalent iodine intermediate 366 foiiowed by recycliza-tion of the resulting acyl cation 367 with the carbonyl oxygen (Scheme 3.146). In a similar procedure,... 

The 2-rhenafuran-3-ol 39 is in equUibrium with the corresponding 37/-furanone 40 (A eq = 1-5) while the equilibrium constant is much more on the side of the furanone when the ring Re is replaced by Mn or in the absence of the metal heteroatom. For example, no 5-methyl-2-furanol (41) is detected in the rearrangement of y-methylene-y-bntyrolactone (42) to a-angehcalactone (43). Understanding the contribution to aromaticity of Re in the 2-rhenafurans (39, 40) and the exocyclic and endocyclic methylene groups in 42 and 43 would be most instructive. 

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