Carbonate protecting group

Synthesis of 1,4-di-Cbz-protected triazonane and further substitution on the position 7 and 1,4-deprotection were reported <2000JOM(611)586>. Methyl carbonate protecting group is easily removed in />-hydroxybenzoyl derivatives of thiadiazonane and dithiazonane by NH4OH <2001JMC1011>. Their further O-acylation gave a variety of derivatives with ester substituents on benzoyl moiety. 

An excerpt from a synthesis of the phytosiderophore Nicotianamine illustrates the formation and cleavage of the 2,2,2-trichloroethyl carbonate protecting group [Scheme 4.357].676 Reaction of alcohol 357,1 with 2,2,2-trichloroethyl chloroformate and a catalytic amount of DMAP in pyridine gave the 2,2>2-tri-chloroethyl carbonate 357 2 in 98% yield. After oxidative destruction of the two p-methoxyphenyl rings to carboxylic acids and esterification, the 2224ri-chloroethyl carbonate 3573 was cleaved with zinc and acetic acid in 97% yield. 

Another example is thermally depolymerizable polycarbonates that are sensitized with onium salt cationic photoinitiators (139). As discussed previously (Section 3.2.3), one of the positive-negative resists based on polystyrene with pendant tertiary butyl carbonate protecting groups undergoes acid-catalyzed thermolysis to generate poly( p-vinylphenol), carbon dioxide, and isobutene. Therefore, if the tertiary butyl carbonate moiety is incorporated in the polymer backbone as a repeating unit, such polymers will... 

At this point, the beauty of the synthesis emerges. Methanolysis of the carbonate protecting group and oxalic acid-catalyzed cyclodehydration of the resulting hydroxy ketone (path a, as shown in Scheme 50) provides 380. Catalytic reduction introduces the remaining two chiral centers to give 381 as the major product (88 9 3). 

The epimeric (+)-a-allokainic acid was constructed by the unsaturated imide/ alkyne alkylative coupling of 9 with trimethylaluminum in 73% yield and 97 3 diastereoselectivity (Scheme 8.11) [33]. This was followed by silyl to carbonate protecting group transposition, stereoselective aUylic reduction, and removal of protecting groups to afford (+)-a-allokainic acid. The complementary nature of these two stereodivergent approaches allowed access to both epimeric natural products. 

Synthesis. - A report on perspectives on alkyl carbonates in organic synthesis has appeared. This contains applications of alkyl carbonate protecting groups in carbohydrate chemistry, carbonate exchange reactions and subsequent modifications as applied to carbohydrate derivatives and promotion of glycosylations. ... 

Elaboration of the D-ring was achieved through the key intermediate 14.1.13, which was converted to an oxetane derivative by the steps of mesylation, osmylation, and treatment with base similar, although not identical pathways were used by all the other workers in this area. The synthesis was completed by conversion of the 1,2-carbonate protective group to the C-2 benzoate (another sequence used by most of the other investigators), and insertion of the C-9 oxygenation to give the protected baccatin III derivative 14.1.17. 

A good example of the use of the cyclic carbonate protecting group is in the synthesis of D-erythrose (108) from methyl /5-D- ucofuranoside 5,6-carbonate (106) [185]. The latter compound, which was prepared by the action of MeOH—Hj SO4 on... 

Ye et al. recently developed another conformation assistance method based on the preactivation protocol of the 2-deoxythioglycosyl donors, which have a carbonate protecting group at C3 and C4, with benzenesulfinyl morpholine... 

FMOC-Cl has been used for 3, 5 -hydroxyl protection of deoxyribose for the introduction of modified bases such as aza-cytidine using the classical Vorbriiggen reaction. While the carbonate protecting groups do not alter the stereoselectivity of the (V-glycoside formation, the FMOC groups can be removed under much milder conditions (EtyN/pyridine) than the typical 4-methylbenzoyl group (eq 9). 

RCM strategy that was thwarted by conformational constraints imposing a cyclic carbonate protecting group of the C1-C2 diol motif. 

---