T-butyldimethylsilyloxy

A. (S)-Ethyl 2-(t-Butyldimethylsilyloxy)propanoate (1). A 2-L, two-necked, round-bottomed flask equipped with a mechanical stirrer and inert gas inlet (Note 1) is charged with (S)-ethyl lactate (118 g, 1.0 mol), 500 mL of dimethylformamide (DMF), and imidazole (102 g, 1.5 mol) (Note 2). The solution is cooled in a ice bath and te/ t-butyldimethy 1 si 1 y 1 chloride (TBDMSC1) (150 g, 1.0 mol) is added in three 50-g portions, at intervals of 30 min between each addition. After the addition of the third portion, a white precipitate forms. The ice bath allowed to melt gradually overnight. After 18 hr, the reaction mixture is diluted with 300 mL of water and 500 mL of hexanes. The aqueous phase is separated and extracted with 300 mL of hexanes, and the combined hexane extracts are washed with three 50-mL portions of saturated brine, dried over MgS04, filtered, and concentrated by rotary evaporation to afford 240 g (103%) of the TBDMS ether as a colorless liquid. The product is distilled under vacuum (bp 70-78°C, 0.5 mm bath temperature 95-105°C) (Note 3) to afford 222 g (96%) of ester 1 as a colorless liquid (Notes 4, 5). 

B. (S)-2-(t-Butyldimethylsilyloxy)propanal (2). A 2-L, single-necked, round-bottomed flask equipped with a large magnetic stirbar, rubber septum, and inert gas inlet (Note 1) is charged with (s)-ethyl 2-(t-butyldimcthylsilyloxy)propanoate (1) (69.9 g, 300 mmol) and 600 mL of hexanes, and cooled in a dry ice-acetone bath at -78°C. A 500-mL, round-bottomed flask equipped with a rubber septum and inert gas inlet is charged with 310 mL of DIBAL-H (1.0M in hexanes, 310 mmol) (Note 6) and cooled to -78°C. The DIBAL-H solution is transferred by cannula into the well-stirred solution of ester over 20... 

The present route to (terminal alkynes reported by a group from the Chemical Process Department at the DuPont Pharmaceutical Company.2 This alcohol serves as a convenient starting material for the preparation of 1-acyloxy 4-mesylates 10 (eq 1). 

The related l-methyl-2-t-butyldimethylsilyloxy allylidenecyclopropane (129) reacted with activated dienophiles at ambient temperature or even below (Table 13, entries 2-4) to give moderate to good yields of the corresponding [4 + 2] cycloadducts 133-135. Only dimethyl acetylenedicarboxylate (113) required heating to 110 ° to give good yields of the adduct 132 (Table 13, entry 1) [32]. Adduct 135 from p-quinone (entry 4) tends to oxidize by purification on silica gel in the air. 

Methyl (E)-4-(t-butyldimethylsilyloxy)-3-methyl-2-butenoate, 187 N-Phenylselenophthalimide, 245 Zinc, 346... 

A TBAF-induced elimination/rearrangement of certain 4- /t-butyldimethylsilyloxy-2-amino-l-aza-bicyclo[4.1.0]-hept-3-enes led to substituted l//-azepin-4(7//)-one derivatives in low to fair yields rearrangement to N-substituted pyrid-(177)-ones was a substituent-dependent competing process <2007T11167>. 

R,5R,6S,8R)-p-Nitrobenzyl-4-methyl-6-(l-hydroxyethyl)-l-azabicyclo [3.2.0]-hept-3,7-dione-2-carboxylate was obtained from 170 mg of 4-(l-carboxy)ethyl-3-[(R)-l-(t-butyldimethylsilyloxy)ethyl]-l-(t-butyldimethylsilyl)-2-azetidinone (3a) according to the method described in Japanese Patent Application OPI No. 26887/83, pages 64-65. 

Figure 2. Synthesis of (1 S,4R)-4-t-butyldimethylsilyloxy-3-chloro-2-cyclopenten-1-ol. Reagents a) PPL (25%) b) PDC/DMF (91%).

A select set of useful [4 + 2] cycloaddition reactions of simple 2-aza-1,3-butadienes have been detailed (Table 11), " and in most instances the 2-azadienes employed are substituted with strong electron-donating substituents responsible for enhancing its Diels-Alder reactivity toward electron-deficient dienophiles. The ease with which the l,3-bis(t-butyldimethylsilyloxy)-2-aza-1,3-butadienes may be prepared from imides, and the demonstrated facility with which they participate in HOMOdiene-controlled [4 + 2] cycloaddition reactions, may prove exceptionally useful their use constitutes the most general approach to implementing the 477 participation of 2-aza-1,3-butadienes (Scheme 12). With the recent introduction of a convenient preparation of 3-trimethylsilyloxy-2-aza-1,3-butadienes, their comparable synthetic utility may be anticipated. ... 

Ab initio and density functional theoretical studies of the 4 -b 2-cycloaddition of 2-azabutadiene with formaldehyde predict a concerted reaction that agrees well with experimental evidence. " The azadiene A-phenyl-l-aza-2-cyanohuta-1,3-diene reacts with electron-rich, electron-poor, and neutral dipolarophiles imder nuld thermal conditions. 5,6-Dihydro-4//-l,2-oxazines have been shown to he useful as synthon equivalents of 2-cyano-l-azabuta-l,3-dienes. The intramolecular Diels-Alder reaction of 1-aza-1,3-butadienes (106) can be activated by a 2-cyano substituent (Scheme 37). Stereoselectivity in the hetero-Diels-Alder reactions of heterobutadienes, nitrosoalkenes, and heterodienophiles has been extensively reviewed. The azadiene l-(t-butyldimethylsilyloxy)-l-azabuta-l,3-diene (107) reacts with halobenzo-quinones, naphthoquinones, and A/ -phenylmaleimide to yield low to good yields of various pyridine heterocycles (108) (Scheme 38). The 4 -b 2-cycloaddition of homophthalic anhydride with A/ -(cinnamylidene)tritylamine produces the 3,4-adduct whereas with A/ -(cinnamylidene)benzylidine the 1,2-adduct is produced. ... 

Similarly prepared were 3-acetoxy-2,3-dihydro-4ff-pyran-4-one (2 Rj = H, Rj = OAc) [from l-methoxy-2-acetoxy-3-trimethylsilyloxy-l,3-butadiene (1 Rj = H, R2 = OAc) and paraformaldehyde in 67% yield] and 5-acetoxy-3-benzoyloxy-2,3-dihydro-4H-pyran-4-one (from l-benzoyloxy-2-t-butyldimethylsilyloxy-3-acetoxy-4-methoxy-l,3-butadiene and paraformaldehyde in 75% yield). 

A)-(t-Butyldimethylsilyloxy)ethyl)-4-[(A)-carboxyethyl]-2- Ci4H27NO4Si Kaneka, Takasago... 

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