"One-pot" access to 4H-chromenes with formation of a chiral quaternary stereogenic center by a highly enantioselective iminium-allenamine involved oxa-Michael-aldol cascade.
Liu, Chunliang; Zhang, Xinshuai; Wang, Rui; Wang, Wei; Organic letters 12 (2010) 4948–4951; doi:10.1021/ol102096s

data_1503266
_publ_section_title
;
 &quot;One-pot&quot; access to 4H-chromenes with formation of a chiral
 quaternary stereogenic center by a highly enantioselective
 iminium-allenamine involved oxa-Michael-aldol cascade.
;
_journal_issue                   21
_journal_name_full               'Organic letters'
_journal_page_first              4948
_journal_page_last               4951
_journal_paper_doi               10.1021/ol102096s
_journal_volume                  12
_journal_year                    2010
_chemical_formula_sum            'C20 H17 Cl O6'
_chemical_formula_weight         388.79
_space_group_IT_number           19
_symmetry_cell_setting           orthorhombic
_symmetry_space_group_name_Hall  'P 2ac 2ab'
_symmetry_space_group_name_H-M   'P 21 21 21'
_atom_sites_solution_hydrogens   geom
_atom_sites_solution_primary     direct
_atom_sites_solution_secondary   difmap
_audit_creation_method           SHELXL-97
_cell_angle_alpha                90.00
_cell_angle_beta                 90.00
_cell_angle_gamma                90.00
_cell_formula_units_Z            4
_cell_length_a                   7.8779(9)
_cell_length_b                   11.7191(14)
_cell_length_c                   20.476(2)
_cell_measurement_reflns_used    4312
_cell_measurement_temperature    296(2)
_cell_measurement_theta_max      24.45
_cell_measurement_theta_min      2.64
_cell_volume                     1890.4(4)
_computing_cell_refinement       'Bruker SAINT'
_computing_data_collection       'Bruker APEX2'
_computing_data_reduction        'Bruker SAINT'
_computing_molecular_graphics    'Bruker SHELXTL'
_computing_publication_material  'Bruker SHELXTL'
_computing_structure_refinement  'SHELXL-97 (Sheldrick, 2008)'
_computing_structure_solution    'SHELXS-97 (Sheldrick, 2008)'
_diffrn_ambient_temperature      296(2)
_diffrn_measured_fraction_theta_full 0.999
_diffrn_measured_fraction_theta_max 0.999
_diffrn_measurement_device_type  'Bruker APEX-II CCD'
_diffrn_measurement_method       '\f and \w scans'
_diffrn_radiation_monochromator  graphite
_diffrn_radiation_source         'fine-focus sealed tube'
_diffrn_radiation_type           MoK\a
_diffrn_radiation_wavelength     0.71073
_diffrn_reflns_av_R_equivalents  0.0298
_diffrn_reflns_av_sigmaI/netI    0.0260
_diffrn_reflns_limit_h_max       9
_diffrn_reflns_limit_h_min       -9
_diffrn_reflns_limit_k_max       14
_diffrn_reflns_limit_k_min       -13
_diffrn_reflns_limit_l_max       24
_diffrn_reflns_limit_l_min       -21
_diffrn_reflns_number            13864
_diffrn_reflns_theta_full        25.50
_diffrn_reflns_theta_max         25.50
_diffrn_reflns_theta_min         2.64
_exptl_absorpt_coefficient_mu    0.236
_exptl_absorpt_correction_T_max  0.9544
_exptl_absorpt_correction_T_min  0.9116
_exptl_absorpt_correction_type   multi-scan
_exptl_crystal_colour            block
_exptl_crystal_density_diffrn    1.366
_exptl_crystal_density_method    'not measured'
_exptl_crystal_description       colourless
_exptl_crystal_F_000             808
_exptl_crystal_size_max          0.40
_exptl_crystal_size_mid          0.32
_exptl_crystal_size_min          0.20
_refine_diff_density_max         0.175
_refine_diff_density_min         -0.212
_refine_diff_density_rms         0.027
_refine_ls_abs_structure_details 'Flack H D (1983), Acta Cryst. A39, 876-881'
_refine_ls_abs_structure_Flack   -0.02(7)
_refine_ls_extinction_coef       0.0119(11)
_refine_ls_extinction_expression Fc^*^=kFc[1+0.001xFc^2^\l^3^/sin(2\q)]^-1/4^
_refine_ls_extinction_method     SHELXL
_refine_ls_goodness_of_fit_ref   1.029
_refine_ls_hydrogen_treatment    constr
_refine_ls_matrix_type           full
_refine_ls_number_parameters     248
_refine_ls_number_reflns         3522
_refine_ls_number_restraints     0
_refine_ls_restrained_S_all      1.029
_refine_ls_R_factor_all          0.0462
_refine_ls_R_factor_gt           0.0356
_refine_ls_shift/su_max          0.001
_refine_ls_shift/su_mean         0.000
_refine_ls_structure_factor_coef Fsqd
_refine_ls_weighting_details
'calc w=1/[\s^2^(Fo^2^)+(0.0376P)^2^+0.2743P] where P=(Fo^2^+2Fc^2^)/3'
_refine_ls_weighting_scheme      calc
_refine_ls_wR_factor_gt          0.0800
_refine_ls_wR_factor_ref         0.0852
_reflns_number_gt                2940
_reflns_number_total             3522
_reflns_threshold_expression     >2sigma(I)
_cod_data_source_file            ol102096s_si_002.cif
_cod_data_source_block           Compound6h
_cod_depositor_comments
;
The following automatic conversions were performed:

'_symmetry_cell_setting' value 'Orthorhombic' changed to
'orthorhombic' according to
/home/saulius/struct/CIF-dictionaries/cif_core.dic dictionary named
'cif_core.dic' version 2.4.2 from 2011-04-26.

Automatic conversion script
Id: cif_fix_values 1715 2011-07-08 13:25:40Z adriana 
;
_cod_original_sg_symbol_H-M      P2(1)2(1)2(1)
_cod_database_code               1503266