5-Methylene-l,3-dioxane

The cycloaddition of methyleneketene 180 with 5-methylene-l,3-dioxane-4,6-dione 181 in principle allows all three double bonds of 180 to react with 181 (Scheme 120) [99JST187]. 

Desymmetrization of 5-methylene-l,3-dioxanes using NiBr2(DIOP)/LiBHEt3 improved the enantioselectivity up to 92% ee (Equation (23)).82... 

The origin of stereofacial selectivity in electrophilic additions to methylene-cyclohexanes (2) and 5-methylene-l,3-dioxane (3) has been elucidated experimentally (Table 2) and theoretically. Ab initio calculations suggest that two electronic factors contribute to the experimentally observed axial stereoselectivity for polarizable electrophiles (in epoxidation and diimide reduction) the spatial anisotropy of the HOMO (common to both molecules) and the anisotropy in the electrostatic potential field (in the case of methylenedioxane). The anisotropy of the HOMO arises from the important topological difference between the contributions made to the HOMO by the periplanar p C-H a-bonds and opposing p C—O or C—C cr-bonds. In contrast, catalytic reduction proceeds with equatorial face selectivity for both the cyclohexane and the dioxane systems and appears to be governed largely by steric effects. ... 

The cycloaddition reaction of methyleneketene 25 and 5-methylene-l,3-dioxan-4,6-dione 26 was studied by DFT at the B3LYP/6-31G" level of theory both in the gas phase and in chloroform solution <1999JMT(488)187>. In the gas phase, the activation barriers for reactions to 27, 28, or 29 (Scheme 1) were calculated to be 21.81, 0.25, and 2.96 kcal mol respectively thus, the reaction leading to the 1,2-adduct 28 was lowest, in agreement with the... 

The reaction of nucleophiles with 1,3-dioxanes containing three double bonds is mainly confined to the group of 5-alkylidene-l,3-dioxane-4,6-diones. The parent compound, 5-methylene-l,3-dioxane-4,6-dione, is, however, quite unstable. Two reagents 170 and 171 have been developed to prepare 5-methylene-l,3-dioxane-4,6-dione in situ (Figure 8) <19968215, 2002SC2009>. 

Methylene-l,3-dioxanes, desymmetrization, 10, 92 y-Methylenefuranones, via silver-catalyzed cycloisomerizations, 9, 561... 

Methylene derivatives, substituted, to protect carbonyl groups, 217 5-Methylene-l,3-dioxanes, to protect carbonyl groups, 186-187 S,S -Methylene dithioacetals, to protect S,Sr-dithiols, 305... 

Alkyl-5-methylene-l,3-dioxanes, 2-f-Butyl-5-methylenetetrahydropyran, and the Corresponding Mcthylcnecyclohexancs"6... 

Methylen-l,3-dioxane werden als Aldehydschutz-Gruppe empfohlen. Sie werden, nach Umlagerung in Enolether, durch milde Saurehydrolyse (THF/1 N Salzsaure 10 1 20°) oder mit Quecksilberchlorid/Quecksilberoxid in waBr. Aceton gespalten221. 

Methylene)-l,3-dioxane-4-ones 19 are formed from aryl acrylates and aliphatic aldehydes in the presence of DABCO via the products 18 of a Baylis-Hillman reaction (cf. p 284) [130] ... 

The reaction of I-naphthyl acrylate with an excess of an aldehyde in CH3CN and in the presence of DABCO leads to 5-methylene-l,3-dioxan-4-ones (Scheme 49) <01CCI6I2>. 

Sanda, F., Fueki, T., Endo, T., 1999. Cationic ring-opening polymerization of an exomethylene group carrying cyclic carbonate. Pseudo-living polymerization of 5-methylene-l,3-dioxan-2-one by the assistance of the exomethylene group. Macromolecules 32, 4220—4224. 

A similar reaction of 5-methylene-l,3-dioxan-2-one with varying amounts of aldehydes afforded monocarbonyl allylation product 1-substituted 2-methylenealkan-l,4-diol or double-carbonyl allylation product 1,5-disubstituted 3-methylenealkan-l,5-diol (eq 54). ... 

Tsuno, T, Sugiyama, K. and Ago, H., A facile epoxidation of 5-methylene-l,3-dioxane-4,6-diones with hydrogen peroxide without catalyst. Heterocycles, 38, 2631-2654, 1994 Tsuno, T. and Sugiyama, K., Addition reaction of photoenols from o-methyl-substituted aromatic ketones with 5-alkylidene-l,3-dioxane-4,6-dione derivatives. Heterocycles, 38, 859-876, 1994 Tsuno, T. and Sugiyama, K., Diels-Alder reaction of photoenol of 2-methylbenzaldehyde with 5-alkylidene-l,3-dioxane-4,6-dione derivatives, iTeterocyc/es, 32,1989-2004, 1991. 

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