STABASE

The commercially available dichlorosilane, 1,2-bis(chlorodimethylsilyl)-ethane, converts primary amines (/) into stabase derivatives ... 

Allylic amines. The stabase adduct (1) of 2-chloroallylamine couples with Grignard reagents in the presence of NiCl2(dppp), dppp = (CfiH )2P(CH2),P(C6H5)2, to form, after deprotection, allylic amines. 

The aldehydes can also be used for a-vinylalion of ketones and esters (equation III) and of amino acids (equation IV) via the stabase derivative (see 1,1,4,4-Tetramethyl-1,4-dichlorodisilelhylene, this volume). 

Scheme 8.232]. Benzostabase derivatives of anilines are appreciably more stable than the parent STABASE analogues, but aliphatic amines show negligible improvement. 

Tetraethyl-1,3-disilaisoindolines (abbreviated TEDI) are about 75 times more stable towards water than the corresponding STABASE derivative and they are more stable to column chromatography. However, they are cleaved in AcOH-EtjO (1 4) with a half-life of 53 minutes,467... 

Pyrrolidines. The Grignard reagent 2, obtained from 3-bromopropylamine protected as the stabase adduct with 1, reacts with the N-methoxy-N-methyl amides 3 (11, 201-202) to form an intermediate ketone that cyclizes to an imine on liberation of the free primary amino group. Reduction of the imine results in a 2-substituted pyrrolidine (4). 

Transmetalation of the ( )-0-Li-enolate derived from the stabase -protected glycine ethyl ester (11) with 1.1 equiv of (1) affords the chiral Ti enolate (12), which adds with high re selectivity to various aldehydes. By mild acidic cleavage of the silyl protecting group, the primary product (13) can be transformed to various Af-derivatives (14) of D-t/treo-a-amino-p-hydroxy acids in 45-66% yield and with excellent enantio- and syn(threo) selectivity (97-99%) (eq 3). An exception with lower enantioselectivity is glyoxylic ester (ethyl ester 78% ee t-butyl ester 87% ee). 

Scheme 73 STABASE and l,l,3,3-Tetramethyl-l,3-disilaisoindoline Adducts of Amino Acid Esters " ...

Recently silicon-based protection has matured into a new Ix oad area of protecting group chemistry (see Section 3.1.3.2) and amines can also be conveniently blocked with appropriate silicon reagents. In organometallic syntheses, e.g. in the alkylation of amino acid enolates, the so-called stabase adducts (30) serve to temporarily protect the a-amino group (Scheme 21). In the absence of hard nucleophiles, in particular of 0-nucleophiles, the Si—N bonds are stable, but deprotection is readily effected in the presence of water and acids. 

Protection of primary amines. Primary amines form the cyclic adducts 2 ( Stabase adducts ) on reaction with 1 and a base (triethylamine for amines with pK 10-11, tt-butyllithium for less basic amines). The adducts are stable to n- and. sec-BuLi (-25°), LDA, H20, CH3OH, KF, and NaHC03 but unstable to HOAc, HC1, KOH, and NaBH. ... 

Sodium trithiocarbonate, 369-370 Spiroannelation, 240, 266-267, 443 Spiro [4.5 ] decadienones, 443 Spiro [4.5 ] decenes, 266-267 Spiro-[4.5]decenones, 100 Spirolactones, 8, 155,192 Stabase adducts, 140 Stannic chloride, 370-373 Stannous chloride-Silver perchlorate, 374 Stannous fluoride, 374 Stannoxanes, 124 Stemodin, 169... 

In an application to asymmetric monobactam synthesis. Overman and Osawa observe a high level of 1,4-diastereofacial selectivity in the reaction of (5)-cyanoamine (235) with the enolate of STABASE-protected glycine ester (234), affording diastereomeric 3-amino-2-azetidinones (236) and (237) in a 10 1 ratio, respectively, and in 65% yield (Scheme 49). Based on the (E)-enolate geometry of glycine ester (234), determined in trapping experiments with TMSCl, the authors postulate a chelated, chair-like transition state (238) that is consistent with the observed stereoselectivity. 

TBS-Protected D-lactaldehyde 961 is used as the chiral source for the synthesis of jS-lactam 969, a key intermediate in the synthesis of the antibiotic monobactam Aztreonam [254] (Scheme 131). The cmcial step in the synthesis, the reaction of A/-trimethylsilylimine 962 with the lithium enolate of STABASE (963), affords ra 5-j5-lactam 964 with 98% diaster-eoselectivity. Desilylation, Jones oxidation, and Baeyer—Villiger oxidation provides acetoxy jS-lactam 968, which in itself is a useful intermediate for the preparation of j5-lactam anti-... 

Space charge limited current (SCLC), 16-9, 16-19, 19-3 Spectral degradation, 5-22, 5-25-5-27 Spin density wave (SDW), 16-12, 16-14 Spiral morphology, 3-3, 3-7-3-S, 3-10-3-12 Spiro linkages, 5-6, 5-20, 5-22, 5-23, 5-24 Spiro-type oligoarylenes, 5-23, 5-24, 5-30 STABASE, 9-21... 

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