4- Methylene-l,3-dioxanes

Two 4-methylene-l,3-dioxane diastereoisomers, isomeric at C-6, were subjected to the rhodium-catalyzed hydro-formylation. The stereochemistry of the newly formed stereogenic carbon was guided solely by the acetal stereocenter (not by C-6) (Scheme 56) <1997JA11118, 1998TL6423>. 

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]. 

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>. 

Dimethyl-5-[(2-hydroxyl-2-phenyl)]methylene-l,3-dioxane-4,6-dione... 

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] ... 

Treatment of 2,4,4-trimethyI-l,3-dioxan under acid conditions gave 5,6-dihydro-2,4-dimethylpyran, but related dioxans also gave some 2,3-dihydro-pyrans. Dihalogenocarbenes, generated by phase-transfer catalysis, effect a regiospecific insertion reaction in 1,3-dioxans (317 R — H, alkyl, or aryl), giving (318). When the methylene-1,3-dioxan (319) is treated with s-butyl-... 

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>. 

Smith utilized Petasis-Ferrier rearrangement [17] in the total syntheses of zampanoUde (Sect. 3.2.1) and phorboxazole [18,19]. The l,3-dioxan-4-ones 11 are transformed into 4-methylene-1,3-dioxanes 12, which are treated with Lewis acids to give oxonium intermediates 13. like the Prins reaction described above, the cfs-2,6-disubstituted tetrahydropyran-3-ones 14 are preferentially synthesized via the C - C bond formation (Scheme 5). 

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. 

The ring interconversion of 1,2-, 1,3-, l,4-ox-4-enes, and ej o-methylene-1,3-dioxanes has been reviewed by Oki (85MI3). 

CH2CH2CH3 poly(vinyl butyral) poly[(2-propyl-l,3-dioxane- 4,6-diyl)methylene]... 

The monomers that have been used for the synthesis include glycolide, lactide, (3-propiolactone, (3-butyro lactone, y-butyrolactone, 6-valerolactone, e-caprol-actone, l,5-dioxepan-2-one, pivalolactone, l,4-dioxane-2-one, 2-methylene-1, 3-dioxolane, 2-methylene-l, 3-dioxepane, etc. The structures of some of these monomers are given in Table 1. 

SYNTHESIS AND [3+2] CYCLOADDITION OF A 2,2-DIALKOXY-l-METHYLENECYCLOPROPANE 6,6-DIMETHYL-l-METHYLENE-4,8-DIOXASPIRO [2.5] OCTANE and cis-5-(5,5-DIMETHYL-l,3-DIOXAN-2-YLIDENE)HEXAHYDRO-l(2H)-PENTALEN-2-ONE... 

D. cis-5-(5,5-Dimethyl-l,3-dioxan-2-ylidene)hexahydro-l(2H)-pentalen-2-one (6). An oven-dried, 50-mL, round-bottomed flask, equipped with a magnetic stirring bar and three-way stopcock, is flushed with nitrogen. A mixture of 6,6-dimethyl-l-methylene-4,8-dioxaspiro[2.5]octane, 5, (8.48 g, 55 mmol) and 2-cyclopenten-1-one (4.52 g, 55 mmol) in 15 mL of acetonitrile is introduced via syringe and the solution is heated at 60°C for 12 hr. The three way stopcock is replaced with a distillation head. Solvent is removed by distillation (ca. 30-120°C/ca. 20-1.4 mm) and the residue is distilled under reduced pressure (142-143°C, 1.4 mm) to afford 6 (10.0 g, 48 mmol, 77%), which crystallizes upon standing at room temperature (Notes 21, 22). 

Esters of halohydrins. Treatment of 2-carboxy-1,3-dioxolanes (1) with phosphorus pentachloride in methylene chloride at room temperature gives esters of 1,2-chloro-hydrins (2) in about 80% yield. Similarly treatment of the 2-carboxy-l,3-dioxane (3) yields an ester of a 1.3-chlorohydrin (4). Reaction of (5 2-carboxy-2-methyl-l,3-... 

---