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Allylic rearrangement in redistribution reactions. the system cis/trans-n-Bu3SnCH2CHCHCH3/n- Bu2SnCl2
No full textAllylic rearrangement occurs in the solvent-free redistribution reaction between trans/cis-Bu3SnCH2CHCHCH3 and Bu2SnCl2:{A figure is presented}. Subsequent isomerization of I is catalyzed by Bu2SnCl2 (see eq. 2) to an equilibrium mixture of cis-II (72-74%) trans-II (12-14%) and I (14-16%) at 30°C as shown by 13C NMR spectroscopy: {A figure is presented}. 13C NMR Spectra also reveal that the terminal olefinic carbon in I is involved in an exchange process. The mechanisms of both reactions probably involve cyclic transition state
Allylstannation III. Synthesis of homoallylic alcohols and 4-chloro-2,6-dialkyl-3-methyltetrahydropyrans by reactions between (E/Z)-2-butenyldichloro-n-butyltin and aldehydes
No full textABSTRACT: 2-Butenyldichloro-n-butyltin (in various cis/trans isomer ratios) reacts readily with neat RCHO (R = CH3, C2H5, (CH3)2CH, and C6H5) at 25°C to give (a) linear alcohols, RCH(OH)CH2CHCHCH3 in the E and Z forms, (b) branched alcohols, RCH(OH)CH(CH3)CHCH2 in the threo and erythro forms, and (c) 2,3,4,6-tetra-substituted tetrahydropyrans (A) as a mixture of cis/trans isomers arising from the CH(CH3)CHCl bond. The maximum yields of these tetrahydropyrans were obtained{A figure is presented} by the use of 3-3.5 molar ratios RCHO/tin compound in the absence of solvent, whereas work-up after reactions in CH2Cl2 gave linear, alcohols as the main products. The formation of linear alcohols appears to be stereospecific, as the ratio of E/Z isomers obtained is the same as that in the organotin compound. Tetrahydropyrans are formed preferentially as the trans isomer
THE PREPARATION OF 4-CHLORO-2,6-DIALKYL-, 4-BROMO-2,6-DIALKYL-, (E/Z)-4-CHLORO-2,6-DIALKYL-3-METHYL-AND (E/Z)-4-BROMO-2,6-DIALKYL-3-METHYL-TETRAHYDROPYRANS BY CONDENSATION OF ALDEHYDES WITH DI-HALIDES AND TRI-HALIDES OF ALLYLTIN .9.
No full textThe reaction recently discovered leading to tetrahydropyrans (THP): has been more extensively investigated by using various allyltin systems, alternate incremental additions of two aldehydes, and scrambling organotin reagents. Unsymmetric halotetrahydropyrans containing various R groups can be readily prepared in this way.
The thermal breakdown of the 12-dichloro adducts, namely (E/Z)1-alkyl-1-butyldichlorostannoxy, 1-alkyl-3-pentyl ethers and the (threo/erythro)-1-alkyl-1-butyldichlorostannoxy, 1-alkyl-2-methyl-3-butenyl ethers, is a stereospecific reaction which affords (E/Z)-halotetrahydropyrans, where the isomerism is at the CHClCH(CH3) bon
Allylchlorotins as allylating agents of acyl chlorides
No full textAllylchlorotins of the type R3-nAllSnCln (R alkyl or All; All CH2CHCH2 or cis/trans-CH3CHCHCH2, n 1-3) undergo uncatalyzed coupling with acyl chlorides under mild conditions. This reaction as well as the corresponding addition reaction to ketones are much faster when Cl is replaced by NCS group in the organotin derivative
Z-Stereoconvergent synthesis of homoallylic alcohols by addition of Bu2ClSnCH(CH3)CHCH2 and α-β-unsaturated aldehydes
No full textBu2ClSnCH(CH3)CHCH2 react with α-β-unsaturated aldehydes to give cis-homoallylic alcohols in high yield
ALLYLSTANNATION .6. ALLYLATION AND ALLENYLATION OF ALDEHYDES AND KETONES BY ALLYL-TIN AND ALLENYL-TIN CHLORIDES IN THE PRESENCE OF WATER
No full textAllyl- and propargyl-carbinols can be readily prepared in one pot reaction, in the presence of water, by addition of allyl- or allenyl-tin chlorides to carbonyl compounds. The reactions of Bu3-n(CH2CHCH2)SnCln, Bu3-n(CH3CHCHCH2)SnCln (n = 1, 2) and Bu2(CH2CCH)SnCl and the carbonyl compounds RCHO (R = H, C2H5, (CH3)2CH, (CH3)3C, (E)-CH3CHCH, C6H5) and RCOR′ (R = R′ = CH3 and R = CH3 and R′ = (CH3)2CH) have been examined. The monochloroorganotin derivatives undergo the following quantitatvive reactions: Bu2(CH2CHCH2)SnCl + RCOR′ + 12H2O → R(HO)C(R′)CH2CHCH2 + 12[Bu2SnCl]2O↓ (1) Bu2(CH2CHCH2)SnCl + RCOR′ + 12H2O → R(HO)C(R′)CH2CHCH + 12[Bu2SnCl]2O↓ (2) Reaction (2), which involves the allenic substrate, is characterized by rearrangement of the unsaturated chain, the propargylic carbinol being isolated as the major product (∼ 90%)
Allylstannation. I. stereochemistry of the addition of trans/cis-2-butenyl-chloro-di-n-butyltin to aldehydes
No full text2-Butenyl-chloro-di-n-butyltin, in various trans/cis ratios, reacts readily with neat RCHO (R = CH3, C2H5, C2H5(CH3)CH, (CH3)2CH, C6H5) at 25°C to give mixtures of threo/erythro-α-methylallylcarbinols in high yields. The same mixtures are obtained from the equilibrated mixtures obtained by redistribution between Bu3SnC4H7 (C4H7 = trans-, cis-crotyl and α-methylallyl group) and Bu2SnCl2. The reactions are characterized by a high degree of stereoselectivity, especially when bulky R groups are present. The complete allylic rearrangement and the stereoselectivity indicate that an exacyclic transition state is involved. Two stereochemically different transition states lead to two diastereoisomers, threo- and ertythro-α-methylallylcarbinol in the enantioforms RS, SR and RR, SS, respectivel
Reversible crotylstannation of carbonyl compounds. Crotylstannation ability of Bu3-nClnSnCH2CHCHCH3 (n = 0, 1, 2) compounds towards acetone and benzaldehyde and 13C NMR characterization
No full textThe crotylstannation reaction: {A figure is presented} has been found to be reversible. The compounds trans/cis-Bu3-nCln SnCH2CH= CHCH3 (n = 0, 1, 2) have been prepared by elimination reactions of organostannoxy compounds,Bu3-nClnSn-O-C(Me)(i-Pr)CH(Me)CHCH2, which were synthesized by means of transalkoxylation between Bu3-nCInSn(OMe) compounds and threo/erithro-2,3,4-trimethyl-5-hexen-3-ol. Under the conditions used the elimination occurs stereospecifically and with complete allylic rearrangement. The ability of the organostannoxy compounds to yield crotyl butylchlorotins via elimination increases in the order, Bu3Sn-O-C < Bu2ClSn-O-C < BuCI2Sn-O-C. In the addition reactions, the sequence of increasing reactivity is Bu3SnCrot < CIBu2SnCrot < CI2BuSnCrot (Crot = crotyl). The 13C NMR spectra of the compounds made reveal that the chemical shifts of the allylic carbon atoms are related to the inductive effects of the chloro-substituent
Allylstannation V. cis-stereoconvergent sysnthesis of homoallylic alcohols and 4-chloro-2,6-dialkyl-3-methyltetrahydro-pyrans by the addition reaction of 1-buten-3-yldichloro-n-butyltin and aldehydes
No full text1-Buten-3-yl-n-butyldichlorotin, generated in situ by redistribution of (E/Z)-2-butenyltri-n-butyltin and BuSnCl3, reacts readily with neat RCHO (R = CH3, C2H5, (CH3)2CH) at 25°C to give linear alcohols RCH(OH)CH2CHCHCH3 and/or 2,3,4,6-tetrasubstituted tetrahydropyrans, CH2CH(R)OCH(R)CH(CH3)CH-(Cl), which are mainly in the cis-configuration with respect to the CH(CH3)-CH(Cl) bond. When R = (CH3)3C and C6H5, only the homoallylic alcohols are obtained. These cis-stereoconvergent syntheses are explained in terms of kinetic control of the formation of adducts obtained by insertion of one or two aldehyde molecules into the organotin substrat
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