Ortho esters, vinyl

Pentaerythritol in rosin ester form is used in hot-melt adhesive formulations, especially ethylene—vinyl acetate (EVA) copolymers, as a tackifier. Polyethers of pentaerythritol or trim ethyl ol eth an e are also used in EVA and polyurethane adhesives, which exhibit excellent bond strength and water resistance. The adhesives maybe available as EVA melts or dispersions (90,91) or as thixotropic, one-package, curable polyurethanes (92). Pentaerythritol spko ortho esters have been used in epoxy resin adhesives (93). The EVA adhesives are especially suitable for cellulose (paper, etc) bonding. 

Enols of simple ketones can be generated in high concentration as metastable species by special techniques. Vinyl alcohol, the enol of acetaldehyde, can be generated by very careful hydrolysis of any of several ortho ester derivatives in which the group RC02 is acetate acid or a chlorinated acetate acid. ... 

The addition of nucleophiles to cyclic fluoroolefins has been reviewed by Park et al. [2 ]. The reaction with alcohols proceeds by addition-elimination to yield the cyclic vinylic ether, as illustrated by tlie reaction of l,2-dichloro-3,3-di-fluorocyclopropene Further reaction results in cyclopropane ring opening at the bond opposite the difluoromethylene carbon to give preferentially the methyl and ortho esters of (Z)-3-chloro-2-fluoroacrylic acid and a small amount of dimethyl malonate [29] (equation 8). 

Stereoselective Claisen-type [3,3] sigmatropic rearrangements of propynyl vinyl ethers, which are intermediates in the reaction of propynyl alcohols with aldehydes or ortho esters leading to a-allenic aldehydes or esters, have been reported15,16. 

Enol Ethers and Esters 0-15 O-Alkylation of carbonyl compounds with diazo alkanes 0-17 Transetherification 0-20 Reaction between acyl halides and active hydrogen compounds 0-23 Transesterification 0-24 Acylation of vinylic halides 0-94 Alkylation with ortho esters 0-107 O-Acylation of 1,3-dicarbonyl compounds... 

More highly vinylically substituted allylic alcohol 9 requires 30 hours at 200 C to give 75% of the ortho ester Claisen product 10.36... 

Ortho ester Claisen rearrangement.2 The [3,3]sigmatropic rearrangement of allyl vinyl alcohols prepared from this ester results in a regiospecific synthesis of diethyl allylmalonates. 

As a silicone mbber membrane is not permeable to hydrophilic or high molecular weight compounds, concerted efforts were made to develop other biocompatible polymers for use in implantable devices. Such polymers include poly(ethylene-co-vinyl acetate), poly (ethylene), poly(propylene), poly(hydroxymethyl methacrylate), poly(lactide-co-glycolide), poly (anhydrides) and poly(ortho esters). The characteristics and applications of each important polymer family will be discussed later in this chapter. 

Which one of the following polymers undergoes homogeneous bulk erosion (a) Poly(lactide-co-glycolide) (b) Poly[bis(p-carboxyphenoxy)propane sebacic acid) (c) Poly(ortho esters) and/or (d) Poly(ethylene-vinyl acetate). 

Lithium aluminum hydride (LAH) does not, as a rule, react with ethers,but does reduce ortho esters to acetals (equation 2). 2-Vinyl-l,3-dioxolane (5) is reduced to a vinyl ether with double-bond rearrangement (equation 3), but the cinnamyl analog (6) is only reduced at the double bond (equation 4). 

In 1988 and 1990, Fuchs reported a new approach to the synthesis of the Cephalotaxus alkaloids ( )-cephalotaxine (1) (30,31), ( )-ll-hydroxyceph-alotaxine (26) (31), and ( )-drupacine (28) (31), which was based on the exploitation of vinyl sulfones as convenient multifunctional synthons (Schemes 7 and 8). The synthesis of cephalotaxine (Scheme 7) began with the ortho ester 77, obtained from piperonyl alcohol in five steps, which was... 

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