Protection, blocking, masking

Propylene carbonate as solvent 20, 413 suppl. 26 Protection, blocking, masking... 

Carreira and co-workers have also extended the scope of aldehydes that may be utilized in catalytic addition reactions to include stannylpropenal 108 as a substrate (Table 8B2.12, Entry 7). The adduct produced from the aldol addition of 105 is isolated with 92% ee and serves as a useful building block, as it is amenable for further synthetic elaboration (Scheme 8B2.9). Thus, vinylstannane 109 is a substrate for Stille cross-coupling reactions to give a diverse family of protected acetoacetate adducts 110. Following deprotection of the masked keto ester, the corresponding hydroxy keto ester 111 may be converted to either the syn or anti skipped polyols 112 or 113. A recent total synthesis of macrolactin A by Carreira and co-workers utilizes aldol... 

Aliphatic aldehydes typically provide only moderate yields in the Biginelli reaction unless special reaction conditions are employed, such as Lewis-acid catalysts or solvent-free methods, or the aldehydes are used in protected form [96]. The C4-unsubstituted DHPM can be prepared in a similar manner employing suitable formaldehyde synthons [96]. Of particular interest are reactions where the aldehyde component is derived from a carbohydrate. In such transformations, DHPMs having a sugar-like moiety in position 4 (C-nucleoside analogues) are obtained (see Section 4.7) [97-106]. Also of interest is the use of masked amino acids as building blocks [107, 108]. In a few cases, bisaldehydes have been used as synthons in Biginelli reactions [89, 109, 110]. 

Fig. 1. Light-directed synthesis of polynucleotide probe arrays. Exposure to light through a photolithographic mask is used to remove protecting groups from surface sites in pre-defined regions of a functionalized glass substrate. A solution of an activated polynucleotide building block is then applied, which reacts specifically in the exposed regions of the substrate. Repeated cycles of illumination-deprotection and monomer coupling are used to construct a two-dimensional array of probe sequences...

The masked disilene procednre was nsed by Saknrai and co-workers to synthesize two samples of diblock copolymers of 1,1-dimethyl-2,2-dihexylsilane (MHS) and 2-(trimethylsilyloxy)ethyl methacrylate, which differed only in the relative lengths of their blocks. Hydrolysis of the trimethylsilyl protecting groups gave the corresponding amphiphilic diblock copolymers, poly(l,l-dimethyl-2,2-dihexyldisilene)-fe-poly(2-hydroxyethyl methacrylate) (PMH S-fc-PHEMA), depicted in Pig. 22 [48]. 

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