[2 + 2]-Photocycloaddition of 1,1-Diethoxyethylene to Chiral Polyfunctional 2-Cyclohexenones. Regioselectivity and π-Facial Discrimination

Abstract

The photochemical [2 + 2]-cycloadditions of 1,1-diethoxyethylene to chiral polyfunctional 2-cyclohexenones have been carried out leading to the production of highly constrained unusual alpha-amino acids with excellent regioselectivity and satisfactory yields. Theoretical calculations have been done to rationalize the observed regio- and diastereoselectivity and show that regiochemistry is determined by the relative rate of formation of the 1,4-biradical intermediates and not by the stability of these species.

Triplet phenacylimidazoliums-catalyzed photocycloaddition of 1,4-dihydropyridines: An experimental and theoretical study

“…At the TS4(T 1 ) associated with the attack of DHP to the DHP-PIm complex, the BO value of the C2 C5 forming bond is 0. 23 is 0.03, which indicates that a significant interaction between DHP and the PIm stabilizes this intermediate. The natural atomic charges have been shared between the DHP and the PIm fragments.…”

“…The two levels of theory used for calculations were the density functional theory (DFT) at Becke's three parameter exchange functional and correlation functional of Lee-Yang-Parr (B3LYP) [20] with the standard 6-31G* basis set [21] for the high level and the semiempirical PM3 method [22] for the low level. This methodology has been successfully applied to study structures and reaction mechanisms for the photocycloaddition between 2-cyclohexenones and 1,1-diethoxyethylene [23]. Open-shell systems have been described within a spin-unrestricted formalism.…”

Cavity Ringdown Spectrum of 2-Cyclohexen-1-one in the CO/Alkenyl CC Stretch Region of the S1(n, π*)–S0 Vibronic Band System

“…Conjugated enone molecules participate in a variety of photochemical processes, including cycloaddition, dissociation, and rearrangement . Several research groups have studied enone photochemistry computationally, − employing economical methods for treating excited electronic states such as complete active-space self-consistent field theory (CASSCF) or time-depedent density functional theory (TDDFT). The computational work has shown that the lowest-energy triplet states, T (π,π*) and T ( n ,π*), typically mediate photochemistry following intersystem crossing from the initially excited S 1 ( n ,π*) state of the enone.…”

Lowest triplet $ {\bm ( n , \pi ^* )}$(n,π*) state of 2-cyclohexen-1-one: Characterization by cavity ringdown spectroscopy and quantum-chemical calculations

“…Computational investigations 2-10 have focused on the participation of cyclic enones, especially 2cyclohexen-1-one (2CHO, Fig. 1), 3,6,7,9 and its substituted derivatives 4,8 in these processes.…”