Addition of α-Substituted (γ-Alkoxyallyl)tins on Aldehydes:  The Dramatic Influence of the Size of the α-Substituent on the Diastereoselection

syn‐Allylstannation of N‐Acyliminium Intermediates by Tributyl[γ‐(silyloxy)allyl]stannanes: A Key Reaction for the Diastereoselective Synthesis of Polyhydroxypiperidines and Polyhydroxyazepanes

“…The different stereochemical outcome obtained in Entries 17 and 18 can be rationalized by the influence of the α-substituent, that is, the bulkier α-substituent induces a higher contribution of TS-B. These results differ with those obtained for the allylstannation of aldehydes, [6] since the anti-selectivity was never highly prevalent. This result can be explained by the higher reactivity of the N-acyliminium species compared to the aldehyde (vide supra) which means that the reaction occurs according to an earlier transition state.…”

“…For this purpose, the readily available γ-oxygenated allyltin compounds E-1a, [21b,23] Z1a, [23] E-1b, [21b,7a] Z-1c, [24] Z-1d, [7a] and Z-1e [7a] have been considered to evaluate their influence on the syn/anti selectivity of the allylstannation reaction, as previously observed with aldehydes (see Table 1). [6,8,9,25] …”

“…[4] However, the synclinal transition state is preferred when steric interactions are involved, in intramolecular allylstannations [5] or when bulky α-substituted γ-(alkoxy)allyltin compounds are involved. [6] The γ-oxygenated allyltin compounds are known as very useful building blocks in the synthesis of polyhydroxylated derivatives. [7] For our part, we have recently considered the addition of [ ‡] dihydroxylation reaction leading to polyhydroxypiperidines or polyhydroxyazepanes in good yields.…”

Crotylation of Aldehydes by Crotyltins: Discrimination between Mechanisms Involving Transmetallation or Simple Lewis Acid Assistance through the Consideration of the Stereochemistry of the Corresponding Homoallylic Alcohols

“…GC (homoallylic alcohols derived from cyclohexanecarbaldehyde): t R = 6.77 (anti), 6.90 (syn), 7.64 (E), 7.74 (Z) min. GC (homoallylic alcohols derived from octanal): t R = 7.25 (anti), 7.34 (syn), 7.89 (E), 8.01 (Z) min.…”

“…[6] However, synclinal transition states can be favoured for instance in intramolecular allylstannations of aldehydes [7] or when γ-alkoxyallyltins containing a bulky α substituent are engaged ( Figure 1). [8] In every case, this condensation of γ-substituted allyltins with aldehydes is an intriguing subject with respect to its regioselectivity (linear α adducts/branched γ adducts) and its stereoselectivity (E/Z ratio in α adducts or syn/anti ratio in γ adducts).…”